Fix use_custom_libcxx=false build on Linux

BUG=None
R=thestig

Change-Id: I17b251faba0e9b8b79fd6b12193add2d61f69c0b
Reviewed-on: https://pdfium-review.googlesource.com/29450
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

samples/pdfium_test_dump_helper.cc

diff --git a/samples/pdfium_test_dump_helper.cc b/samples/pdfium_test_dump_helper.cc
index 5d7af1c..729a4cd 100644
--- a/samples/pdfium_test_dump_helper.cc
+++ b/samples/pdfium_test_dump_helper.cc
@@ -4,6 +4,10 @@
 
 #include "samples/pdfium_test_dump_helper.h"
 
+#include <string.h>
+
+#include <algorithm>
+#include <memory>
 #include <string>
 #include <utility>
 

samples/pdfium_test_write_helper.cc

diff --git a/samples/pdfium_test_write_helper.cc b/samples/pdfium_test_write_helper.cc
index a323658..5a2e0f6 100644
--- a/samples/pdfium_test_write_helper.cc
+++ b/samples/pdfium_test_write_helper.cc
@@ -4,6 +4,8 @@
 
 #include "samples/pdfium_test_write_helper.h"
 
+#include <limits.h>
+
 #include <memory>
 #include <vector>