Fix IWYU errors in fpdfppo.cpp.

Also rename the file to fpdf_ppo.cpp so it is consistent with the public
header file name. This makes the linter happy.

Change-Id: Ib3608c78111842579898c55f1399982ab2549310
Reviewed-on: https://pdfium-review.googlesource.com/24970
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 54aa448..988d376 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -136,6 +136,7 @@
     "fpdfsdk/fpdf_dataavail.cpp",
     "fpdfsdk/fpdf_ext.cpp",
     "fpdfsdk/fpdf_flatten.cpp",
+    "fpdfsdk/fpdf_ppo.cpp",
     "fpdfsdk/fpdf_progressive.cpp",
     "fpdfsdk/fpdf_searchex.cpp",
     "fpdfsdk/fpdf_structtree.cpp",
@@ -150,7 +151,6 @@
     "fpdfsdk/fpdfeditpath.cpp",
     "fpdfsdk/fpdfedittext.cpp",
     "fpdfsdk/fpdfformfill.cpp",
-    "fpdfsdk/fpdfppo.cpp",
     "fpdfsdk/fpdfsave.cpp",
     "fpdfsdk/fpdftext.cpp",
     "fpdfsdk/fpdfview.cpp",
diff --git a/fpdfsdk/fpdfppo.cpp b/fpdfsdk/fpdf_ppo.cpp
similarity index 99%
rename from fpdfsdk/fpdfppo.cpp
rename to fpdfsdk/fpdf_ppo.cpp
index 3e6f099..b5e128f 100644
--- a/fpdfsdk/fpdfppo.cpp
+++ b/fpdfsdk/fpdf_ppo.cpp
@@ -6,6 +6,7 @@
 
 #include "public/fpdf_ppo.h"
 
+#include <algorithm>
 #include <map>
 #include <memory>
 #include <utility>