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:

[scroggo_chromium, 2016/06/06 14:51:40]

Did you also apply the intel patch?

[msarett, 2016/06/06 18:01:57]

Ahh yes, added bullet here.

-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

[scroggo_chromium, 2016/06/06 14:51:40]

Is there an interesting section of pnglibconf.h (which is a large file)? The
version used by Skia is mostly a copy/rename of pnglibconf.h.prebuilt.
(Actually, now that I look at it again, we no longer turn on/off any features,
so it's just a rename, plus it's out of date (specifies the wrong version...).)

It would be helpful if there was a section that is just the features we turned
off at the end.

[msarett, 2016/06/06 18:01:57]

Yes, agreed!  I've rearranged the file to group together "default settings" and
"chromium settings".

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