Update libpng to 1.6.22

third_party/libpng/README.chromium

Index: third_party/libpng/README.chromium
diff --git a/third_party/libpng/README.chromium b/third_party/libpng/README.chromium
index e767a00e4bb5d831d9571900839d29d74e182a1b..a89eb20cc15b965fb7bece9c82d54858ba18a58f 100644
--- a/third_party/libpng/README.chromium
+++ b/third_party/libpng/README.chromium
@@ -1,17 +1,21 @@
 Name: libpng
 URL: http://libpng.org/
-Version: 1.2.56
+Version: 1.6.22
 Security Critical: yes
 License: libpng license
 License Android Compatible: yes
 
 Description:
-Updated to 1.2.56, no changes to the source files but all unneeded files
-stripped.
+Updated to 1.6.22, stripped all unneeded files.
 
-Our custom configuration options are defined in pngusr.h. This was previously
-called mozpngconf.h, which was copied from Mozilla and modified by Apple (hence
-the wk_* names):
-- Unset PNG_NO_READ_PACK on Android in pngusr.h, required by freetype to support
-  color glyphs.
-- Configure PNG chunk user limits (crbug.com/117369)
+- Use custom configuration file pnglibconf.h, which turns off all features that

[Nico, 2016/06/03 20:27:45]

aha; list that in the gyp / gn files then

[msarett, 2016/06/03 21:26:01]

Done!

+  are not in use.
+- Use custom prefix file pngprefix.h, which avoids namespace conflicts with
+  pdfium's copy of libpng.

[Nico, 2016/06/03 20:27:45]

i think pdfium is supposed to use chromium's libpng when it's part of a chromium
build and its own copy else. both copies should never compete with each other.

[msarett, 2016/06/03 21:26:01]

That seems to make sense.  I did try to compile without prefixing, and things
failed to link due to namespace conflicts.  So I decided to leave the prefixing
as is for now.

[Nico, 2016/06/03 21:36:49]

What exactly fails? That sounds like something we should probably fix.

[msarett, 2016/06/06 14:18:15]

../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_access_version_number'
../../third_party/binutils/Linux_x64/Release/bin/ld.gold:
obj/third_party/pdfium/third_party/fx_lpng/png.o: previous definition here
../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_build_gamma_table'
../../third_party/binutils/Linux_x64/Release/bin/ld.gold:
obj/third_party/pdfium/third_party/fx_lpng/png.o: previous definition here
../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_calculate_crc'
../../third_party/binutils/Linux_x64/Release/bin/ld.gold:
obj/third_party/pdfium/third_party/fx_lpng/png.o: previous definition here
../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_check_IHDR'
../../third_party/binutils/Linux_x64/Release/bin/ld.gold:
obj/third_party/pdfium/third_party/fx_lpng/png.o: previous definition here
../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_chunk_unknown_handling'
../../third_party/binutils/Linux_x64/Release/bin/ld.gold:
obj/third_party/pdfium/third_party/fx_lpng/png.o: previous definition here
../../third_party/binutils/Linux_x64/Release/bin/ld.gold: error:
obj/third_party/libpng/libpng_sources/png.o: multiple definition of
'png_colorspace_set_ICC'

etc...
Agreed.  I'm guessing we would need to modify the pdfium build files to only
compile their own copy of libpng when not on Chrome?  Can I handle this in a
follow-up change?

+- Configures custom png chunk user limits (crbug.com/117369) in pnglibconf.h.
+- Fix for potential memory leak from upstream:
+  https://github.com/glennrp/libpng/commit/8d1672537324d99c6e65eb78fc1678cdd46f75bd
+  https://github.com/glennrp/libpng/commit/6c7459e455a4f7d95c7700e9326bb12396e6eb1f
+- Fix for handling empty first IDAT chunk from upstream:
+  https://github.com/glennrp/libpng/commit/3f46c67c6989f480bd932428aa1705f6625dbabf
+  https://github.com/glennrp/libpng/commit/81f0273d54aa9de663253b197b3c8228d659cc36