diff --git a/core/fdrm/fx_crypt_unittest.cpp b/core/fdrm/fx_crypt_unittest.cpp
index a499bd4..77e7705 100644
--- a/core/fdrm/fx_crypt_unittest.cpp
+++ b/core/fdrm/fx_crypt_unittest.cpp
@@ -11,7 +11,7 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/utils/hash.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/cmaps/CNS1/cmaps_cns1.cpp b/core/fpdfapi/cmaps/CNS1/cmaps_cns1.cpp
index a9b305e..00f9571 100644
--- a/core/fpdfapi/cmaps/CNS1/cmaps_cns1.cpp
+++ b/core/fpdfapi/cmaps/CNS1/cmaps_cns1.cpp
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/cmaps/CNS1/cmaps_cns1.h"
 
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 const FXCMAP_CMap g_FXCMAP_CNS1_cmaps[] = {
     {"B5pc-H", g_FXCMAP_B5pc_H_0, nullptr, 247, 0, FXCMAP_CMap::Range, 0},
diff --git a/core/fpdfapi/cmaps/GB1/cmaps_gb1.cpp b/core/fpdfapi/cmaps/GB1/cmaps_gb1.cpp
index fb0e46f..e7ea47e 100644
--- a/core/fpdfapi/cmaps/GB1/cmaps_gb1.cpp
+++ b/core/fpdfapi/cmaps/GB1/cmaps_gb1.cpp
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/cmaps/GB1/cmaps_gb1.h"
 
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 const FXCMAP_CMap g_FXCMAP_GB1_cmaps[] = {
     {"GB-EUC-H", g_FXCMAP_GB_EUC_H_0, nullptr, 90, 0, FXCMAP_CMap::Range, 0},
diff --git a/core/fpdfapi/cmaps/Japan1/cmaps_japan1.cpp b/core/fpdfapi/cmaps/Japan1/cmaps_japan1.cpp
index cbb7be5..03673a4 100644
--- a/core/fpdfapi/cmaps/Japan1/cmaps_japan1.cpp
+++ b/core/fpdfapi/cmaps/Japan1/cmaps_japan1.cpp
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/cmaps/Japan1/cmaps_japan1.h"
 
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 const FXCMAP_CMap g_FXCMAP_Japan1_cmaps[] = {
     {"83pv-RKSJ-H", g_FXCMAP_83pv_RKSJ_H_1, nullptr, 222, 0, FXCMAP_CMap::Range,
diff --git a/core/fpdfapi/cmaps/Korea1/cmaps_korea1.cpp b/core/fpdfapi/cmaps/Korea1/cmaps_korea1.cpp
index b28e971..8eff8cb 100644
--- a/core/fpdfapi/cmaps/Korea1/cmaps_korea1.cpp
+++ b/core/fpdfapi/cmaps/Korea1/cmaps_korea1.cpp
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/cmaps/Korea1/cmaps_korea1.h"
 
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 const FXCMAP_CMap g_FXCMAP_Korea1_cmaps[] = {
     {"KSC-EUC-H", g_FXCMAP_KSC_EUC_H_0, nullptr, 467, 0, FXCMAP_CMap::Range, 0},
diff --git a/core/fpdfapi/edit/cpdf_pagecontentgenerator_unittest.cpp b/core/fpdfapi/edit/cpdf_pagecontentgenerator_unittest.cpp
index 041384f..c9eb746 100644
--- a/core/fpdfapi/edit/cpdf_pagecontentgenerator_unittest.cpp
+++ b/core/fpdfapi/edit/cpdf_pagecontentgenerator_unittest.cpp
@@ -26,7 +26,7 @@
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "core/fxge/cfx_fillrenderoptions.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 class CPDF_PageContentGeneratorTest : public testing::Test {
  protected:
diff --git a/core/fpdfapi/font/cfx_stockfontarray.cpp b/core/fpdfapi/font/cfx_stockfontarray.cpp
index e6ed0f9..50fc1ef 100644
--- a/core/fpdfapi/font/cfx_stockfontarray.cpp
+++ b/core/fpdfapi/font/cfx_stockfontarray.cpp
@@ -8,8 +8,8 @@
 
 #include "core/fpdfapi/font/cpdf_font.h"
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
-#include "third_party/base/stl_util.h"
 
 CFX_StockFontArray::CFX_StockFontArray() = default;
 
diff --git a/core/fpdfapi/font/cpdf_cidfont.cpp b/core/fpdfapi/font/cpdf_cidfont.cpp
index 9aa3127..9785aca 100644
--- a/core/fpdfapi/font/cpdf_cidfont.cpp
+++ b/core/fpdfapi/font/cpdf_cidfont.cpp
@@ -27,6 +27,7 @@
 #include "core/fxge/fx_font.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/core/fpdfapi/font/cpdf_cmapparser.cpp b/core/fpdfapi/font/cpdf_cmapparser.cpp
index a6ce69d..ee16bfa 100644
--- a/core/fpdfapi/font/cpdf_cmapparser.cpp
+++ b/core/fpdfapi/font/cpdf_cmapparser.cpp
@@ -14,7 +14,7 @@
 #include "core/fxcrt/fx_safe_types.h"
 #include "core/fxge/fx_freetype.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/font/cpdf_font.cpp b/core/fpdfapi/font/cpdf_font.cpp
index ddf3d21..c6ea201 100644
--- a/core/fpdfapi/font/cpdf_font.cpp
+++ b/core/fpdfapi/font/cpdf_font.cpp
@@ -30,6 +30,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/fx_freetype.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/core/fpdfapi/font/cpdf_fontencoding.cpp b/core/fpdfapi/font/cpdf_fontencoding.cpp
index 3ebcb6c..c456b60 100644
--- a/core/fpdfapi/font/cpdf_fontencoding.cpp
+++ b/core/fpdfapi/font/cpdf_fontencoding.cpp
@@ -13,7 +13,7 @@
 #include "core/fpdfapi/parser/fpdf_parser_decode.h"
 #include "core/fxge/fx_font.h"
 #include "core/fxge/fx_freetype.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/font/cpdf_simplefont.cpp b/core/fpdfapi/font/cpdf_simplefont.cpp
index 4fc72ed..822cf28 100644
--- a/core/fpdfapi/font/cpdf_simplefont.cpp
+++ b/core/fpdfapi/font/cpdf_simplefont.cpp
@@ -11,8 +11,8 @@
 #include "core/fpdfapi/parser/cpdf_name.h"
 #include "core/fxge/fx_font.h"
 #include "core/fxge/fx_freetype.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/numerics/safe_math.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/core/fpdfapi/font/cpdf_truetypefont.cpp b/core/fpdfapi/font/cpdf_truetypefont.cpp
index a02b872..a200232 100644
--- a/core/fpdfapi/font/cpdf_truetypefont.cpp
+++ b/core/fpdfapi/font/cpdf_truetypefont.cpp
@@ -8,7 +8,7 @@
 
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
 #include "core/fxge/fx_font.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/font/cpdf_type3font.cpp b/core/fpdfapi/font/cpdf_type3font.cpp
index 8631cbf..a6f3bb9 100644
--- a/core/fpdfapi/font/cpdf_type3font.cpp
+++ b/core/fpdfapi/font/cpdf_type3font.cpp
@@ -17,7 +17,7 @@
 #include "core/fxcrt/autorestorer.h"
 #include "core/fxcrt/fx_system.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/page/cpdf_colorspace.cpp b/core/fpdfapi/page/cpdf_colorspace.cpp
index af6d8e6..c6ac14b 100644
--- a/core/fpdfapi/page/cpdf_colorspace.cpp
+++ b/core/fpdfapi/page/cpdf_colorspace.cpp
@@ -36,6 +36,7 @@
 #include "core/fxcrt/scoped_set_insertion.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/core/fpdfapi/page/cpdf_docpagedata.cpp b/core/fpdfapi/page/cpdf_docpagedata.cpp
index 70d4581..410e1c4 100644
--- a/core/fpdfapi/page/cpdf_docpagedata.cpp
+++ b/core/fpdfapi/page/cpdf_docpagedata.cpp
@@ -39,6 +39,7 @@
 #include "core/fxge/cfx_unicodeencoding.h"
 #include "core/fxge/fx_font.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/core/fpdfapi/page/cpdf_psengine_unittest.cpp b/core/fpdfapi/page/cpdf_psengine_unittest.cpp
index 85c77c8..e5f3d3b 100644
--- a/core/fpdfapi/page/cpdf_psengine_unittest.cpp
+++ b/core/fpdfapi/page/cpdf_psengine_unittest.cpp
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/page/cpdf_psengine.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/page/cpdf_streamcontentparser.cpp b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
index 3b883a6..4912d02 100644
--- a/core/fpdfapi/page/cpdf_streamcontentparser.cpp
+++ b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
@@ -39,6 +39,7 @@
 #include "core/fxcrt/scoped_set_insertion.h"
 #include "core/fxge/cfx_graphstatedata.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/no_destructor.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/span.h"
diff --git a/core/fpdfapi/parser/cpdf_array_unittest.cpp b/core/fpdfapi/parser/cpdf_array_unittest.cpp
index 23b3f5c..0d6f2ba 100644
--- a/core/fpdfapi/parser/cpdf_array_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_array_unittest.cpp
@@ -11,7 +11,7 @@
 #include "core/fpdfapi/parser/cpdf_number.h"
 #include "core/fpdfapi/parser/cpdf_reference.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(cpdf_array, GetBooleanAt) {
   auto arr = pdfium::MakeRetain<CPDF_Array>();
diff --git a/core/fpdfapi/parser/cpdf_object_unittest.cpp b/core/fpdfapi/parser/cpdf_object_unittest.cpp
index 0e8da80..29fcdf3 100644
--- a/core/fpdfapi/parser/cpdf_object_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_object_unittest.cpp
@@ -23,7 +23,7 @@
 #include "core/fpdfapi/parser/cpdf_string.h"
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/parser/cpdf_parser_unittest.cpp b/core/fpdfapi/parser/cpdf_parser_unittest.cpp
index b32f8c9..9e0cbd9 100644
--- a/core/fpdfapi/parser/cpdf_parser_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_parser_unittest.cpp
@@ -18,7 +18,7 @@
 #include "core/fxcrt/retain_ptr.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/utils/path_service.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfapi/parser/cpdf_security_handler.cpp b/core/fpdfapi/parser/cpdf_security_handler.cpp
index d9201e7..747cc2e 100644
--- a/core/fpdfapi/parser/cpdf_security_handler.cpp
+++ b/core/fpdfapi/parser/cpdf_security_handler.cpp
@@ -21,8 +21,8 @@
 #include "core/fxcrt/fx_random.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/core/fpdfapi/parser/cpdf_simple_parser_unittest.cpp b/core/fpdfapi/parser/cpdf_simple_parser_unittest.cpp
index 580668a..482ce6e 100644
--- a/core/fpdfapi/parser/cpdf_simple_parser_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_simple_parser_unittest.cpp
@@ -7,8 +7,8 @@
 #include "core/fpdfapi/parser/fpdf_parser_utility.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
-#include "third_party/base/stl_util.h"
 
 TEST(SimpleParserTest, GetWord) {
   static const pdfium::StrFuncTestData test_data[] = {
diff --git a/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp b/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
index bd1b423..f0660e6 100644
--- a/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
+++ b/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
@@ -11,7 +11,7 @@
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(fpdf_parser_decode, ValidateDecoderPipeline) {
   {
diff --git a/core/fpdfapi/render/cpdf_docrenderdata_unittest.cpp b/core/fpdfapi/render/cpdf_docrenderdata_unittest.cpp
index 98b3926..685b706 100644
--- a/core/fpdfapi/render/cpdf_docrenderdata_unittest.cpp
+++ b/core/fpdfapi/render/cpdf_docrenderdata_unittest.cpp
@@ -14,7 +14,7 @@
 #include "core/fpdfapi/parser/cpdf_stream.h"
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfdoc/cpdf_aaction.cpp b/core/fpdfdoc/cpdf_aaction.cpp
index e0ae9e9..edc1b01 100644
--- a/core/fpdfdoc/cpdf_aaction.cpp
+++ b/core/fpdfdoc/cpdf_aaction.cpp
@@ -7,7 +7,7 @@
 #include "core/fpdfdoc/cpdf_aaction.h"
 
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfdoc/cpdf_action.cpp b/core/fpdfdoc/cpdf_action.cpp
index 87e0f28..e8b4058 100644
--- a/core/fpdfdoc/cpdf_action.cpp
+++ b/core/fpdfdoc/cpdf_action.cpp
@@ -12,7 +12,7 @@
 #include "core/fpdfapi/parser/cpdf_document.h"
 #include "core/fpdfapi/parser/cpdf_name.h"
 #include "core/fpdfdoc/cpdf_filespec.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfdoc/cpdf_defaultappearance_unittest.cpp b/core/fpdfdoc/cpdf_defaultappearance_unittest.cpp
index 58c3e6d..7dfa940 100644
--- a/core/fpdfdoc/cpdf_defaultappearance_unittest.cpp
+++ b/core/fpdfdoc/cpdf_defaultappearance_unittest.cpp
@@ -6,8 +6,8 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
-#include "third_party/base/stl_util.h"
 
 TEST(CPDFDefaultAppearanceTest, FindTagParamFromStart) {
   static const struct FindTagTestStruct {
diff --git a/core/fpdfdoc/cpdf_dest.cpp b/core/fpdfdoc/cpdf_dest.cpp
index 3740723..bb4e16a 100644
--- a/core/fpdfdoc/cpdf_dest.cpp
+++ b/core/fpdfdoc/cpdf_dest.cpp
@@ -13,7 +13,7 @@
 #include "core/fpdfapi/parser/cpdf_name.h"
 #include "core/fpdfapi/parser/cpdf_number.h"
 #include "core/fpdfdoc/cpdf_nametree.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdfdoc/cpdf_filespec.cpp b/core/fpdfdoc/cpdf_filespec.cpp
index 63148ee..5194d2f 100644
--- a/core/fpdfdoc/cpdf_filespec.cpp
+++ b/core/fpdfdoc/cpdf_filespec.cpp
@@ -16,8 +16,8 @@
 #include "core/fpdfapi/parser/fpdf_parser_decode.h"
 #include "core/fxcrt/fx_system.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/core/fpdfdoc/cpdf_filespec_unittest.cpp b/core/fpdfdoc/cpdf_filespec_unittest.cpp
index 3a2359a..16a3b94 100644
--- a/core/fpdfdoc/cpdf_filespec_unittest.cpp
+++ b/core/fpdfdoc/cpdf_filespec_unittest.cpp
@@ -16,7 +16,7 @@
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(cpdf_filespec, EncodeDecodeFileName) {
   static const std::vector<pdfium::NullTermWstrFuncTestData> test_data = {
diff --git a/core/fpdfdoc/cpdf_formcontrol.cpp b/core/fpdfdoc/cpdf_formcontrol.cpp
index da4b425..875b65b 100644
--- a/core/fpdfdoc/cpdf_formcontrol.cpp
+++ b/core/fpdfdoc/cpdf_formcontrol.cpp
@@ -16,7 +16,7 @@
 #include "core/fpdfapi/parser/fpdf_parser_utility.h"
 #include "core/fpdfdoc/cpdf_interactiveform.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fpdftext/cpdf_linkextract_unittest.cpp b/core/fpdftext/cpdf_linkextract_unittest.cpp
index 316f039..f1528fa 100644
--- a/core/fpdftext/cpdf_linkextract_unittest.cpp
+++ b/core/fpdftext/cpdf_linkextract_unittest.cpp
@@ -5,7 +5,7 @@
 #include "core/fpdftext/cpdf_linkextract.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 // Class to help test functions in CPDF_LinkExtract class.
 class CPDF_TestLinkExtract final : public CPDF_LinkExtract {
diff --git a/core/fxcodec/basic/a85_unittest.cpp b/core/fxcodec/basic/a85_unittest.cpp
index 109adda..782e0b4 100644
--- a/core/fxcodec/basic/a85_unittest.cpp
+++ b/core/fxcodec/basic/a85_unittest.cpp
@@ -10,7 +10,7 @@
 #include "core/fxcodec/basic/basicmodule.h"
 #include "core/fxcrt/fx_memory_wrappers.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(fxcodec, A85TestBadInputs) {
   const uint8_t src_buf[] = {1, 2, 3, 4};
diff --git a/core/fxcodec/gif/cfx_gifcontext.cpp b/core/fxcodec/gif/cfx_gifcontext.cpp
index 907c05d..af8e175 100644
--- a/core/fxcodec/gif/cfx_gifcontext.cpp
+++ b/core/fxcodec/gif/cfx_gifcontext.cpp
@@ -10,6 +10,7 @@
 #include <utility>
 
 #include "core/fxcodec/cfx_codec_memory.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace fxcodec {
diff --git a/core/fxcodec/gif/lzw_decompressor_unittest.cpp b/core/fxcodec/gif/lzw_decompressor_unittest.cpp
index 3434beb..99e186e 100644
--- a/core/fxcodec/gif/lzw_decompressor_unittest.cpp
+++ b/core/fxcodec/gif/lzw_decompressor_unittest.cpp
@@ -5,7 +5,7 @@
 #include "core/fxcodec/gif/lzw_decompressor.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(LZWDecompressor, CreateBadParams) {
   EXPECT_EQ(nullptr, LZWDecompressor::Create(0x10, 0x02));
diff --git a/core/fxcodec/jbig2/JBig2_ArithDecoder.cpp b/core/fxcodec/jbig2/JBig2_ArithDecoder.cpp
index 16d5c13..0aec465 100644
--- a/core/fxcodec/jbig2/JBig2_ArithDecoder.cpp
+++ b/core/fxcodec/jbig2/JBig2_ArithDecoder.cpp
@@ -8,7 +8,7 @@
 
 #include "core/fxcodec/jbig2/JBig2_BitStream.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fxcodec/jbig2/JBig2_ArithIntDecoder.cpp b/core/fxcodec/jbig2/JBig2_ArithIntDecoder.cpp
index b2cd8aa..89478f6 100644
--- a/core/fxcodec/jbig2/JBig2_ArithIntDecoder.cpp
+++ b/core/fxcodec/jbig2/JBig2_ArithIntDecoder.cpp
@@ -9,7 +9,7 @@
 #include <vector>
 
 #include "core/fxcrt/fx_safe_types.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp b/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
index 054aba8..409053f 100644
--- a/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
+++ b/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
@@ -12,7 +12,7 @@
 #include "core/fxcodec/jbig2/JBig2_Context.h"
 #include "core/fxcrt/fx_safe_types.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fxcrt/cfx_seekablestreamproxy_unittest.cpp b/core/fxcrt/cfx_seekablestreamproxy_unittest.cpp
index 2448e81..a20ecff 100644
--- a/core/fxcrt/cfx_seekablestreamproxy_unittest.cpp
+++ b/core/fxcrt/cfx_seekablestreamproxy_unittest.cpp
@@ -7,8 +7,8 @@
 #include "core/fxcrt/cfx_readonlymemorystream.h"
 #include "core/fxcrt/retain_ptr.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
-#include "third_party/base/stl_util.h"
 
 TEST(SeekableStreamProxyTest, NullStream) {
   auto proxy_stream = pdfium::MakeRetain<CFX_SeekableStreamProxy>(
diff --git a/core/fxcrt/fx_coordinates.cpp b/core/fxcrt/fx_coordinates.cpp
index dfaa89a..eebbc20 100644
--- a/core/fxcrt/fx_coordinates.cpp
+++ b/core/fxcrt/fx_coordinates.cpp
@@ -11,6 +11,7 @@
 #include "build/build_config.h"
 #include "core/fxcrt/fx_extension.h"
 #include "core/fxcrt/fx_safe_types.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 #ifndef NDEBUG
diff --git a/core/fxcrt/fx_extension_unittest.cpp b/core/fxcrt/fx_extension_unittest.cpp
index 74a63f0..fd03ab2 100644
--- a/core/fxcrt/fx_extension_unittest.cpp
+++ b/core/fxcrt/fx_extension_unittest.cpp
@@ -7,7 +7,7 @@
 #include <limits>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(fxcrt, FXSYS_IsLowerASCII) {
   EXPECT_TRUE(FXSYS_IsLowerASCII('a'));
diff --git a/core/fxcrt/fx_string.cpp b/core/fxcrt/fx_string.cpp
index 3fa80e4..2e22b70 100644
--- a/core/fxcrt/fx_string.cpp
+++ b/core/fxcrt/fx_string.cpp
@@ -10,7 +10,7 @@
 #include "core/fxcrt/cfx_utf8encoder.h"
 #include "core/fxcrt/fx_extension.h"
 #include "third_party/base/compiler_specific.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 ByteString FX_UTF8Encode(WideStringView wsStr) {
   CFX_UTF8Encoder encoder;
diff --git a/core/fxcrt/fx_system_unittest.cpp b/core/fxcrt/fx_system_unittest.cpp
index 2b51c15..5a44aad 100644
--- a/core/fxcrt/fx_system_unittest.cpp
+++ b/core/fxcrt/fx_system_unittest.cpp
@@ -8,7 +8,7 @@
 #include "core/fxcrt/fx_string.h"
 #include "core/fxcrt/fx_system.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 // Unit test covering cases where PDFium replaces well-known library
 // functionality on any given platformn.
diff --git a/core/fxcrt/fx_unicode.cpp b/core/fxcrt/fx_unicode.cpp
index 77562b3..2983655 100644
--- a/core/fxcrt/fx_unicode.cpp
+++ b/core/fxcrt/fx_unicode.cpp
@@ -7,7 +7,7 @@
 #include "core/fxcrt/fx_unicode.h"
 
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fxcrt/widestring_unittest.cpp b/core/fxcrt/widestring_unittest.cpp
index 640d11c..02cd488 100644
--- a/core/fxcrt/widestring_unittest.cpp
+++ b/core/fxcrt/widestring_unittest.cpp
@@ -11,6 +11,7 @@
 #include "build/build_config.h"
 #include "core/fxcrt/fx_string.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/core/fxge/android/cfpf_skiafontmgr.cpp b/core/fxge/android/cfpf_skiafontmgr.cpp
index b75d12f..424251f 100644
--- a/core/fxge/android/cfpf_skiafontmgr.cpp
+++ b/core/fxge/android/cfpf_skiafontmgr.cpp
@@ -18,6 +18,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/fx_freetype.h"
 #include "third_party/base/containers/adapters.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/core/fxge/cfx_folderfontinfo.cpp b/core/fxge/cfx_folderfontinfo.cpp
index 6109370..a062cbf 100644
--- a/core/fxge/cfx_folderfontinfo.cpp
+++ b/core/fxge/cfx_folderfontinfo.cpp
@@ -17,6 +17,7 @@
 #include "core/fxcrt/fx_stream.h"
 #include "core/fxge/cfx_fontmapper.h"
 #include "core/fxge/fx_font.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/core/fxge/cfx_font.cpp b/core/fxge/cfx_font.cpp
index 472e7a7..4a0df96 100644
--- a/core/fxge/cfx_font.cpp
+++ b/core/fxge/cfx_font.cpp
@@ -25,6 +25,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/scoped_font_transform.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/core/fxge/cfx_fontmapper.cpp b/core/fxge/cfx_fontmapper.cpp
index e605c55..973e099 100644
--- a/core/fxge/cfx_fontmapper.cpp
+++ b/core/fxge/cfx_fontmapper.cpp
@@ -22,6 +22,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/systemfontinfo_iface.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/core/fxge/cfx_fontmgr.cpp b/core/fxge/cfx_fontmgr.cpp
index a15da5e..e0ff166 100644
--- a/core/fxge/cfx_fontmgr.cpp
+++ b/core/fxge/cfx_fontmgr.cpp
@@ -16,7 +16,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/systemfontinfo_iface.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/core/fxge/dib/cfx_dibbase.cpp b/core/fxge/dib/cfx_dibbase.cpp
index d8be60d..4ec0ddb 100644
--- a/core/fxge/dib/cfx_dibbase.cpp
+++ b/core/fxge/dib/cfx_dibbase.cpp
@@ -20,9 +20,9 @@
 #include "core/fxge/dib/cfx_imagetransformer.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/span.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/core/fxge/dib/cfx_imagetransformer.cpp b/core/fxge/dib/cfx_imagetransformer.cpp
index 9a328e9..35abf58 100644
--- a/core/fxge/dib/cfx_imagetransformer.cpp
+++ b/core/fxge/dib/cfx_imagetransformer.cpp
@@ -15,9 +15,9 @@
 #include "core/fxge/dib/fx_dib.h"
 #include "third_party/base/check.h"
 #include "third_party/base/compiler_specific.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/numerics/safe_conversions.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/core/fxge/linux/fx_linux_impl.cpp b/core/fxge/linux/fx_linux_impl.cpp
index bfd4375..bda2a7d 100644
--- a/core/fxge/linux/fx_linux_impl.cpp
+++ b/core/fxge/linux/fx_linux_impl.cpp
@@ -15,6 +15,7 @@
 #include "core/fxge/fx_font.h"
 #include "core/fxge/systemfontinfo_iface.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 #if !defined(OS_LINUX) && !defined(OS_CHROMEOS) && !defined(OS_ASMJS)
diff --git a/core/fxge/win32/cgdi_plus_ext.cpp b/core/fxge/win32/cgdi_plus_ext.cpp
index 9be3371..51db123 100644
--- a/core/fxge/win32/cgdi_plus_ext.cpp
+++ b/core/fxge/win32/cgdi_plus_ext.cpp
@@ -25,8 +25,9 @@
 #include "core/fxge/cfx_path.h"
 #include "core/fxge/dib/cfx_dibitmap.h"
 #include "core/fxge/win32/cwin32_platform.h"
+#include "third_party/base/cxx17_backports.h"
+#include "third_party/base/numerics/safe_conversions.h"
 #include "third_party/base/span.h"
-#include "third_party/base/stl_util.h"
 
 // Has to come before gdiplus.h
 namespace Gdiplus {
diff --git a/core/fxge/win32/cwin32_platform.cpp b/core/fxge/win32/cwin32_platform.cpp
index c45d426..c04aa1b 100644
--- a/core/fxge/win32/cwin32_platform.cpp
+++ b/core/fxge/win32/cwin32_platform.cpp
@@ -11,6 +11,7 @@
 #include "core/fxcrt/fx_codepage.h"
 #include "core/fxge/cfx_folderfontinfo.h"
 #include "core/fxge/cfx_gemodule.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/ptr_util.h"
 #include "third_party/base/stl_util.h"
 #include "third_party/base/win/win_util.h"
diff --git a/fpdfsdk/cpdfsdk_appstream.cpp b/fpdfsdk/cpdfsdk_appstream.cpp
index c1b34b8..2d01282 100644
--- a/fpdfsdk/cpdfsdk_appstream.cpp
+++ b/fpdfsdk/cpdfsdk_appstream.cpp
@@ -32,7 +32,7 @@
 #include "fpdfsdk/pwl/cpwl_edit.h"
 #include "fpdfsdk/pwl/cpwl_edit_impl.h"
 #include "fpdfsdk/pwl/cpwl_wnd.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fpdfsdk/fpdf_annot.cpp b/fpdfsdk/fpdf_annot.cpp
index da569c4..73be990 100644
--- a/fpdfsdk/fpdf_annot.cpp
+++ b/fpdfsdk/fpdf_annot.cpp
@@ -34,6 +34,7 @@
 #include "fpdfsdk/cpdfsdk_helpers.h"
 #include "fpdfsdk/cpdfsdk_interactiveform.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/ptr_util.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/fpdfsdk/fpdf_annot_embeddertest.cpp b/fpdfsdk/fpdf_annot_embeddertest.cpp
index 8dd050e..ceeb020 100644
--- a/fpdfsdk/fpdf_annot_embeddertest.cpp
+++ b/fpdfsdk/fpdf_annot_embeddertest.cpp
@@ -30,6 +30,7 @@
 #include "testing/gmock/include/gmock/gmock-matchers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/utils/hash.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/span.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/fpdfsdk/fpdf_formfill_embeddertest.cpp b/fpdfsdk/fpdf_formfill_embeddertest.cpp
index 2ee5136..2414bc8 100644
--- a/fpdfsdk/fpdf_formfill_embeddertest.cpp
+++ b/fpdfsdk/fpdf_formfill_embeddertest.cpp
@@ -21,7 +21,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 using pdfium::kTextFormChecksum;
 
diff --git a/fpdfsdk/fpdf_ppo_embeddertest.cpp b/fpdfsdk/fpdf_ppo_embeddertest.cpp
index 84d52e9..85751c1 100644
--- a/fpdfsdk/fpdf_ppo_embeddertest.cpp
+++ b/fpdfsdk/fpdf_ppo_embeddertest.cpp
@@ -12,7 +12,7 @@
 #include "public/fpdfview.h"
 #include "testing/embedder_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fpdfsdk/fpdf_signature_embeddertest.cpp b/fpdfsdk/fpdf_signature_embeddertest.cpp
index db31990..317ef24 100644
--- a/fpdfsdk/fpdf_signature_embeddertest.cpp
+++ b/fpdfsdk/fpdf_signature_embeddertest.cpp
@@ -7,7 +7,7 @@
 #include "public/fpdf_signature.h"
 #include "testing/embedder_test.h"
 #include "testing/fx_string_testhelpers.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 class FPDFSignatureEmbedderTest : public EmbedderTest {};
 
diff --git a/fpdfsdk/fpdf_structtree_embeddertest.cpp b/fpdfsdk/fpdf_structtree_embeddertest.cpp
index f447fbb..9906928 100644
--- a/fpdfsdk/fpdf_structtree_embeddertest.cpp
+++ b/fpdfsdk/fpdf_structtree_embeddertest.cpp
@@ -6,8 +6,8 @@
 #include "public/fpdf_structtree.h"
 #include "testing/embedder_test.h"
 #include "testing/fx_string_testhelpers.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/optional.h"
-#include "third_party/base/stl_util.h"
 
 class FPDFStructTreeEmbedderTest : public EmbedderTest {};
 
diff --git a/fpdfsdk/fpdf_text_embeddertest.cpp b/fpdfsdk/fpdf_text_embeddertest.cpp
index 73754ec..4b653bd 100644
--- a/fpdfsdk/fpdf_text_embeddertest.cpp
+++ b/fpdfsdk/fpdf_text_embeddertest.cpp
@@ -16,7 +16,7 @@
 #include "testing/embedder_test.h"
 #include "testing/fx_string_testhelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fpdfsdk/fpdf_view_embeddertest.cpp b/fpdfsdk/fpdf_view_embeddertest.cpp
index 9c16bc7..0099cb7 100644
--- a/fpdfsdk/fpdf_view_embeddertest.cpp
+++ b/fpdfsdk/fpdf_view_embeddertest.cpp
@@ -23,7 +23,7 @@
 #include "testing/utils/hash.h"
 #include "testing/utils/path_service.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 using pdfium::kManyRectanglesChecksum;
 
diff --git a/fpdfsdk/pwl/cpwl_sbbutton.cpp b/fpdfsdk/pwl/cpwl_sbbutton.cpp
index f2fbd52..a75ac99 100644
--- a/fpdfsdk/pwl/cpwl_sbbutton.cpp
+++ b/fpdfsdk/pwl/cpwl_sbbutton.cpp
@@ -10,7 +10,7 @@
 #include <vector>
 
 #include "core/fxge/cfx_renderdevice.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 CPWL_SBButton::CPWL_SBButton(
     const CreateParams& cp,
diff --git a/fxbarcode/datamatrix/BC_C40Encoder.cpp b/fxbarcode/datamatrix/BC_C40Encoder.cpp
index 8cdc2d1..1f783c7 100644
--- a/fxbarcode/datamatrix/BC_C40Encoder.cpp
+++ b/fxbarcode/datamatrix/BC_C40Encoder.cpp
@@ -29,7 +29,7 @@
 #include "fxbarcode/datamatrix/BC_HighLevelEncoder.h"
 #include "fxbarcode/datamatrix/BC_SymbolInfo.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fxbarcode/datamatrix/BC_DataMatrixWriter_unittest.cpp b/fxbarcode/datamatrix/BC_DataMatrixWriter_unittest.cpp
index 90c738f..b6009fc 100644
--- a/fxbarcode/datamatrix/BC_DataMatrixWriter_unittest.cpp
+++ b/fxbarcode/datamatrix/BC_DataMatrixWriter_unittest.cpp
@@ -7,7 +7,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 class CBC_DataMatrixWriterTest : public testing::Test {
  public:
diff --git a/fxbarcode/datamatrix/BC_ErrorCorrection.cpp b/fxbarcode/datamatrix/BC_ErrorCorrection.cpp
index 7713a48..c3a87d1 100644
--- a/fxbarcode/datamatrix/BC_ErrorCorrection.cpp
+++ b/fxbarcode/datamatrix/BC_ErrorCorrection.cpp
@@ -29,7 +29,7 @@
 #include "fxbarcode/datamatrix/BC_Encoder.h"
 #include "fxbarcode/datamatrix/BC_SymbolInfo.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fxbarcode/datamatrix/BC_SymbolInfo.cpp b/fxbarcode/datamatrix/BC_SymbolInfo.cpp
index 06031cf..7bec809 100644
--- a/fxbarcode/datamatrix/BC_SymbolInfo.cpp
+++ b/fxbarcode/datamatrix/BC_SymbolInfo.cpp
@@ -25,8 +25,8 @@
 #include "fxbarcode/common/BC_CommonBitMatrix.h"
 #include "fxbarcode/datamatrix/BC_DataMatrixSymbolInfo144.h"
 #include "fxbarcode/datamatrix/BC_Encoder.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
-#include "third_party/base/stl_util.h"
 
 namespace {
 
diff --git a/fxbarcode/oned/BC_OnedCodaBarWriter.cpp b/fxbarcode/oned/BC_OnedCodaBarWriter.cpp
index 816d39c..56b6da9 100644
--- a/fxbarcode/oned/BC_OnedCodaBarWriter.cpp
+++ b/fxbarcode/oned/BC_OnedCodaBarWriter.cpp
@@ -27,6 +27,7 @@
 #include "fxbarcode/BC_Writer.h"
 #include "fxbarcode/common/BC_CommonBitMatrix.h"
 #include "fxbarcode/oned/BC_OneDimWriter.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/fxbarcode/oned/BC_OnedCode128Writer_unittest.cpp b/fxbarcode/oned/BC_OnedCode128Writer_unittest.cpp
index d17e989..c39bf28 100644
--- a/fxbarcode/oned/BC_OnedCode128Writer_unittest.cpp
+++ b/fxbarcode/oned/BC_OnedCode128Writer_unittest.cpp
@@ -5,7 +5,7 @@
 #include "fxbarcode/oned/BC_OnedCode128Writer.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fxbarcode/oned/BC_OnedCode39Writer.cpp b/fxbarcode/oned/BC_OnedCode39Writer.cpp
index 7f2de96..754124b 100644
--- a/fxbarcode/oned/BC_OnedCode39Writer.cpp
+++ b/fxbarcode/oned/BC_OnedCode39Writer.cpp
@@ -30,7 +30,7 @@
 #include "fxbarcode/BC_Writer.h"
 #include "fxbarcode/common/BC_CommonBitMatrix.h"
 #include "fxbarcode/oned/BC_OneDimWriter.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp b/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp
index 1e1ed1f..7f75536 100644
--- a/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp
+++ b/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp
@@ -7,7 +7,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(PDF417HighLevelEncoderTest, EncodeHighLevel) {
   static constexpr struct EncodeHighLevelCase {
diff --git a/fxbarcode/pdf417/BC_PDF417Writer_unittest.cpp b/fxbarcode/pdf417/BC_PDF417Writer_unittest.cpp
index 6851f24..ac06eec 100644
--- a/fxbarcode/pdf417/BC_PDF417Writer_unittest.cpp
+++ b/fxbarcode/pdf417/BC_PDF417Writer_unittest.cpp
@@ -7,7 +7,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 class CBC_PDF417WriterTest : public testing::Test {
  public:
diff --git a/fxbarcode/qrcode/BC_QRCodeWriter_unittest.cpp b/fxbarcode/qrcode/BC_QRCodeWriter_unittest.cpp
index 227d242..43855a7 100644
--- a/fxbarcode/qrcode/BC_QRCodeWriter_unittest.cpp
+++ b/fxbarcode/qrcode/BC_QRCodeWriter_unittest.cpp
@@ -7,7 +7,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 class CBC_QRCodeWriterTest : public testing::Test {
  public:
diff --git a/fxbarcode/qrcode/BC_QRCoderEncoder.cpp b/fxbarcode/qrcode/BC_QRCoderEncoder.cpp
index 0b68642..5873107 100644
--- a/fxbarcode/qrcode/BC_QRCoderEncoder.cpp
+++ b/fxbarcode/qrcode/BC_QRCoderEncoder.cpp
@@ -40,8 +40,8 @@
 #include "fxbarcode/qrcode/BC_QRCoderVersion.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/optional.h"
-#include "third_party/base/stl_util.h"
 
 using ModeStringPair = std::pair<CBC_QRCoderMode*, ByteString>;
 
diff --git a/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp b/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
index 356e7f5..11008d9 100644
--- a/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
+++ b/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
@@ -29,7 +29,7 @@
 #include "fxbarcode/qrcode/BC_QRCoderMaskUtil.h"
 #include "third_party/base/check.h"
 #include "third_party/base/check_op.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/fxjs/cjs_globalarrays.cpp b/fxjs/cjs_globalarrays.cpp
index 72f7439..0ec2671 100644
--- a/fxjs/cjs_globalarrays.cpp
+++ b/fxjs/cjs_globalarrays.cpp
@@ -6,7 +6,7 @@
 
 #include "fxjs/cjs_globalarrays.h"
 
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 #define GLOBAL_ARRAY(rt, name, ...)                                          \
   {                                                                          \
diff --git a/fxjs/cjs_publicmethods.cpp b/fxjs/cjs_publicmethods.cpp
index be25e17..f7e9429 100644
--- a/fxjs/cjs_publicmethods.cpp
+++ b/fxjs/cjs_publicmethods.cpp
@@ -35,6 +35,7 @@
 #include "fxjs/js_define.h"
 #include "fxjs/js_resources.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/optional.h"
 #include "third_party/base/stl_util.h"
 
diff --git a/fxjs/cjs_publicmethods_unittest.cpp b/fxjs/cjs_publicmethods_unittest.cpp
index 69ba63a..95fdbd8 100644
--- a/fxjs/cjs_publicmethods_unittest.cpp
+++ b/fxjs/cjs_publicmethods_unittest.cpp
@@ -5,7 +5,7 @@
 #include "fxjs/cjs_publicmethods.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(CJS_PublicMethods, IsNumber) {
   // TODO(weili): Check whether results from case 0, 1, 10, 15 are intended.
diff --git a/fxjs/cjs_util.cpp b/fxjs/cjs_util.cpp
index dfd40de..5440869 100644
--- a/fxjs/cjs_util.cpp
+++ b/fxjs/cjs_util.cpp
@@ -26,7 +26,7 @@
 #include "fxjs/js_define.h"
 #include "fxjs/js_resources.h"
 #include "third_party/base/check_op.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 #if defined(OS_ANDROID)
 #include <ctype.h>
diff --git a/fxjs/cjs_util_unittest.cpp b/fxjs/cjs_util_unittest.cpp
index 77fa270..39b7318 100644
--- a/fxjs/cjs_util_unittest.cpp
+++ b/fxjs/cjs_util_unittest.cpp
@@ -5,7 +5,7 @@
 #include "fxjs/cjs_util.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(CJS_Util, ParseDataType) {
   struct ParseDataTypeCase {
diff --git a/fxjs/fx_date_helpers.cpp b/fxjs/fx_date_helpers.cpp
index 24d6890..2240a87 100644
--- a/fxjs/fx_date_helpers.cpp
+++ b/fxjs/fx_date_helpers.cpp
@@ -14,6 +14,7 @@
 #include "core/fxcrt/fx_extension.h"
 #include "core/fxcrt/fx_system.h"
 #include "fpdfsdk/cpdfsdk_helpers.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace fxjs {
diff --git a/fxjs/xfa/cfxjse_formcalc_context.cpp b/fxjs/xfa/cfxjse_formcalc_context.cpp
index c2d623e..17ff8ad 100644
--- a/fxjs/xfa/cfxjse_formcalc_context.cpp
+++ b/fxjs/xfa/cfxjse_formcalc_context.cpp
@@ -24,6 +24,7 @@
 #include "fxjs/xfa/cfxjse_value.h"
 #include "fxjs/xfa/cjx_object.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/optional.h"
 #include "third_party/base/stl_util.h"
 #include "xfa/fgas/crt/cfgas_decimal.h"
diff --git a/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp b/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
index d356aaf..64d535f 100644
--- a/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
+++ b/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
@@ -11,7 +11,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/scoped_set_tz.h"
 #include "testing/xfa_js_embedder_test.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "xfa/fxfa/cxfa_eventparam.h"
 
 class CFXJSE_FormCalcContextEmbedderTest : public XFAJSEmbedderTest {
diff --git a/testing/fuzzers/pdf_cfgas_stringformatter_fuzzer.cc b/testing/fuzzers/pdf_cfgas_stringformatter_fuzzer.cc
index 481f286..06a3424 100644
--- a/testing/fuzzers/pdf_cfgas_stringformatter_fuzzer.cc
+++ b/testing/fuzzers/pdf_cfgas_stringformatter_fuzzer.cc
@@ -13,7 +13,7 @@
 #include "public/fpdfview.h"
 #include "testing/fuzzers/pdfium_fuzzer_util.h"
 #include "testing/fuzzers/xfa_process_state.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "v8/include/cppgc/heap.h"
 #include "v8/include/cppgc/persistent.h"
 #include "xfa/fxfa/parser/cxfa_localemgr.h"
diff --git a/testing/fuzzers/pdf_scanlinecompositor_fuzzer.cc b/testing/fuzzers/pdf_scanlinecompositor_fuzzer.cc
index 0a698f1..9a9d735 100644
--- a/testing/fuzzers/pdf_scanlinecompositor_fuzzer.cc
+++ b/testing/fuzzers/pdf_scanlinecompositor_fuzzer.cc
@@ -9,7 +9,7 @@
 #include "core/fxge/dib/cfx_dibitmap.h"
 #include "core/fxge/dib/fx_dib.h"
 #include "testing/fuzzers/pdfium_fuzzer_util.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index f2c5999..4e6e940 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -596,6 +596,7 @@
     "base/check_op.h",
     "base/compiler_specific.h",
     "base/containers/adapters.h",
+    "base/cxx17_backports.h",
     "base/debug/alias.cc",
     "base/debug/alias.h",
     "base/immediate_crash.h",
diff --git a/third_party/base/allocator/partition_allocator/partition_alloc.h b/third_party/base/allocator/partition_allocator/partition_alloc.h
index 483c75e..ca091b6 100644
--- a/third_party/base/allocator/partition_allocator/partition_alloc.h
+++ b/third_party/base/allocator/partition_allocator/partition_alloc.h
@@ -75,7 +75,7 @@
 #include "third_party/base/bits.h"
 #include "third_party/base/check.h"
 #include "third_party/base/compiler_specific.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/sys_byteorder.h"
 
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
diff --git a/third_party/base/cxx17_backports.h b/third_party/base/cxx17_backports.h
new file mode 100644
index 0000000..de1ab07
--- /dev/null
+++ b/third_party/base/cxx17_backports.h
@@ -0,0 +1,24 @@
+// Copyright 2021 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef THIRD_PARTY_BASE_CXX17_BACKPORTS_H_
+#define THIRD_PARTY_BASE_CXX17_BACKPORTS_H_
+
+namespace pdfium {
+
+// C++14 implementation of C++17's std::size():
+// http://en.cppreference.com/w/cpp/iterator/size
+template <typename Container>
+constexpr auto size(const Container& c) -> decltype(c.size()) {
+  return c.size();
+}
+
+template <typename T, size_t N>
+constexpr size_t size(const T (&array)[N]) noexcept {
+  return N;
+}
+
+}  // namespace pdfium
+
+#endif  // THIRD_PARTY_BASE_CXX17_BACKPORTS_H_
diff --git a/third_party/base/stl_util.h b/third_party/base/stl_util.h
index 40ae622..169fed4 100644
--- a/third_party/base/stl_util.h
+++ b/third_party/base/stl_util.h
@@ -53,18 +53,6 @@
 
 }  // namespace internal
 
-// C++14 implementation of C++17's std::size():
-// http://en.cppreference.com/w/cpp/iterator/size
-template <typename Container>
-constexpr auto size(const Container& c) -> decltype(c.size()) {
-  return c.size();
-}
-
-template <typename T, size_t N>
-constexpr size_t size(const T (&array)[N]) noexcept {
-  return N;
-}
-
 // General purpose implementation to check if |container| contains |value|.
 template <typename Container,
           typename Value,
diff --git a/xfa/fde/cfde_wordbreak_data.cpp b/xfa/fde/cfde_wordbreak_data.cpp
index 1856cc5..2e1a3f0 100644
--- a/xfa/fde/cfde_wordbreak_data.cpp
+++ b/xfa/fde/cfde_wordbreak_data.cpp
@@ -8,7 +8,7 @@
 
 #include "core/fxcrt/fx_system.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/xfa/fgas/crt/cfgas_stringformatter.cpp b/xfa/fgas/crt/cfgas_stringformatter.cpp
index 94b8223..b119b4f 100644
--- a/xfa/fgas/crt/cfgas_stringformatter.cpp
+++ b/xfa/fgas/crt/cfgas_stringformatter.cpp
@@ -14,6 +14,7 @@
 #include "core/fxcrt/cfx_datetime.h"
 #include "core/fxcrt/fx_extension.h"
 #include "core/fxcrt/fx_safe_types.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/stl_util.h"
 #include "xfa/fgas/crt/cfgas_decimal.h"
diff --git a/xfa/fgas/crt/cfgas_stringformatter_unittest.cpp b/xfa/fgas/crt/cfgas_stringformatter_unittest.cpp
index f60d283..183d967 100644
--- a/xfa/fgas/crt/cfgas_stringformatter_unittest.cpp
+++ b/xfa/fgas/crt/cfgas_stringformatter_unittest.cpp
@@ -13,7 +13,7 @@
 #include "testing/fxgc_unittest.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/scoped_set_tz.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "v8/include/cppgc/persistent.h"
 #include "xfa/fxfa/parser/cxfa_localemgr.h"
 
diff --git a/xfa/fgas/font/cfgas_fontmgr.cpp b/xfa/fgas/font/cfgas_fontmgr.cpp
index 0f8064a..be95390 100644
--- a/xfa/fgas/font/cfgas_fontmgr.cpp
+++ b/xfa/fgas/font/cfgas_fontmgr.cpp
@@ -20,6 +20,7 @@
 #include "core/fxge/cfx_gemodule.h"
 #include "core/fxge/fx_font.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 #include "xfa/fgas/font/cfgas_gefont.h"
 #include "xfa/fgas/font/fgas_fontutils.h"
diff --git a/xfa/fgas/font/cfgas_pdffontmgr.cpp b/xfa/fgas/font/cfgas_pdffontmgr.cpp
index 3f97d65..ba60799 100644
--- a/xfa/fgas/font/cfgas_pdffontmgr.cpp
+++ b/xfa/fgas/font/cfgas_pdffontmgr.cpp
@@ -14,6 +14,7 @@
 #include "core/fpdfapi/parser/cpdf_document.h"
 #include "core/fxge/fx_font.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 #include "xfa/fgas/font/cfgas_fontmgr.h"
 #include "xfa/fgas/font/cfgas_gefont.h"
diff --git a/xfa/fgas/font/fgas_fontutils.cpp b/xfa/fgas/font/fgas_fontutils.cpp
index 2c50e3b..191aeb8 100644
--- a/xfa/fgas/font/fgas_fontutils.cpp
+++ b/xfa/fgas/font/fgas_fontutils.cpp
@@ -9,7 +9,7 @@
 #include "build/build_config.h"
 #include "core/fxcrt/fx_codepage.h"
 #include "core/fxcrt/fx_extension.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "xfa/fgas/font/cfgas_fontmgr.h"
 
 namespace {
diff --git a/xfa/fgas/graphics/cfgas_gegraphics.cpp b/xfa/fgas/graphics/cfgas_gegraphics.cpp
index b9721ed..c92db6a 100644
--- a/xfa/fgas/graphics/cfgas_gegraphics.cpp
+++ b/xfa/fgas/graphics/cfgas_gegraphics.cpp
@@ -14,7 +14,7 @@
 #include "core/fxge/cfx_unicodeencoding.h"
 #include "core/fxge/dib/cfx_dibitmap.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "xfa/fgas/graphics/cfgas_gecolor.h"
 #include "xfa/fgas/graphics/cfgas_gepath.h"
 #include "xfa/fgas/graphics/cfgas_gepattern.h"
diff --git a/xfa/fgas/layout/cfgas_char.cpp b/xfa/fgas/layout/cfgas_char.cpp
index db53a96..e060aae 100644
--- a/xfa/fgas/layout/cfgas_char.cpp
+++ b/xfa/fgas/layout/cfgas_char.cpp
@@ -10,6 +10,7 @@
 
 #include "core/fxcrt/fx_extension.h"
 #include "third_party/base/check.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 
 namespace {
diff --git a/xfa/fgas/layout/fgas_arabic.cpp b/xfa/fgas/layout/fgas_arabic.cpp
index 0790011..0242e39 100644
--- a/xfa/fgas/layout/fgas_arabic.cpp
+++ b/xfa/fgas/layout/fgas_arabic.cpp
@@ -7,7 +7,7 @@
 #include "xfa/fgas/layout/fgas_arabic.h"
 
 #include "core/fxcrt/fx_unicode.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "xfa/fgas/layout/cfgas_char.h"
 
 namespace {
diff --git a/xfa/fgas/layout/fgas_linebreak.cpp b/xfa/fgas/layout/fgas_linebreak.cpp
index cc82483..7c34681 100644
--- a/xfa/fgas/layout/fgas_linebreak.cpp
+++ b/xfa/fgas/layout/fgas_linebreak.cpp
@@ -8,7 +8,7 @@
 
 #include "core/fxcrt/fx_unicode.h"
 #include "third_party/base/check.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 namespace {
 
diff --git a/xfa/fwl/theme/cfwl_checkboxtp.cpp b/xfa/fwl/theme/cfwl_checkboxtp.cpp
index a19927e..ee4e4e4 100644
--- a/xfa/fwl/theme/cfwl_checkboxtp.cpp
+++ b/xfa/fwl/theme/cfwl_checkboxtp.cpp
@@ -7,7 +7,7 @@
 #include "xfa/fwl/theme/cfwl_checkboxtp.h"
 
 #include "core/fxge/cfx_path.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 #include "xfa/fde/cfde_textout.h"
 #include "xfa/fgas/graphics/cfgas_gecolor.h"
 #include "xfa/fgas/graphics/cfgas_gepath.h"
diff --git a/xfa/fxfa/fm2js/cxfa_fmlexer_unittest.cpp b/xfa/fxfa/fm2js/cxfa_fmlexer_unittest.cpp
index 6ecc3b9..6f4cd49 100644
--- a/xfa/fxfa/fm2js/cxfa_fmlexer_unittest.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fmlexer_unittest.cpp
@@ -8,7 +8,7 @@
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(CXFA_FMLexerTest, NullString) {
   WideStringView null_string;
diff --git a/xfa/fxfa/parser/xfa_basic_data.cpp b/xfa/fxfa/parser/xfa_basic_data.cpp
index c2d5b73..92f2e49 100644
--- a/xfa/fxfa/parser/xfa_basic_data.cpp
+++ b/xfa/fxfa/parser/xfa_basic_data.cpp
@@ -40,6 +40,7 @@
 #include "fxjs/xfa/cjx_treelist.h"
 #include "fxjs/xfa/cjx_wsdlconnection.h"
 #include "fxjs/xfa/cjx_xfa.h"
+#include "third_party/base/cxx17_backports.h"
 #include "third_party/base/stl_util.h"
 #include "xfa/fxfa/fxfa_basic.h"
 
diff --git a/xfa/fxfa/parser/xfa_utils_unittest.cpp b/xfa/fxfa/parser/xfa_utils_unittest.cpp
index 7cdbd74..5493ce4 100644
--- a/xfa/fxfa/parser/xfa_utils_unittest.cpp
+++ b/xfa/fxfa/parser/xfa_utils_unittest.cpp
@@ -5,7 +5,7 @@
 #include "xfa/fxfa/parser/xfa_utils.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/base/stl_util.h"
+#include "third_party/base/cxx17_backports.h"
 
 TEST(XfaUtilsImpTest, XFA_MapRotation) {
   struct TestCase {