Update libpng to 1.6.22rc01

DEPS

 use_relative_paths = True
 
 # Dependencies on outside packages.
 #
 deps = {
   "common": "https://skia.googlesource.com/common.git@c282fe0b6e392b14f88d647cbd86e1a3ef5498e0",
 
   # There is some duplication here that might be worth cleaning up:
   #   - can use use our existing t_p/e/libjpeg instead of pulling it for Android?
 
   "third_party/externals/angle2"  : "https://chromium.googlesource.com/angle/angle.git@8182049470aa3ba0c9f7c54ef965bf1877df08cb",
   "third_party/externals/cmake"   : "https://cmake.googlesource.com/cmake.git@v3.3.1",
   "third_party/externals/freetype": "https://skia.googlesource.com/third_party/freetype2.git@6a19a7d332c5446542196e5aeda0ede109ef097b",
   "third_party/externals/gyp"     : "https://chromium.googlesource.com/external/gyp.git@87ac4d0e63fc7dd8152a350327fea8dcf031bf56",
   "third_party/externals/harfbuzz": "https://skia.googlesource.com/third_party/harfbuzz.git@1.2.7",
   "third_party/externals/jsoncpp" : "https://chromium.googlesource.com/external/github.com/open-source-parsers/jsoncpp.git@1.0.0",
   "third_party/externals/libwebp" : "https://chromium.googlesource.com/webm/libwebp.git@v0.5.0",
   "third_party/externals/nanomsg" : "https://skia.googlesource.com/third_party/nanomsg.git@0.4-beta",
   "third_party/externals/zlib"    : "https://chromium.googlesource.com/chromium/src/third_party/zlib@c4e33043fb071b6ea0a153845da625d7ed633d3d",
   # NOTE: If we update libpng, we may need to update the generated file at third_party/libpng/pnglibconf.h
-  "third_party/externals/libpng"  : "https://skia.googlesource.com/third_party/libpng.git@5765a2224946b953ec6702bd01205af475f8c80a",
+  "third_party/externals/libpng"  : "https://github.com/mattsarett/libpng.git@393063051764f2410daf931e8f414f37e157f7a1",

[msarett, 2016/05/16 14:14:16]

It's strange to clone from github/mattsarett.

We can't use the libpng mirror because there is now one extra config step.  We
need to run the following command to enable the Intel optimizations.

patch -i contrib/intel/intel_sse.patch -p1

[scroggo, 2016/05/16 19:20:45]

So does this mean we'll have to continue to use the github/mattsarett version?
I'm surprised that libpng is making us do a patch to enable these. It seems like
it would be cleaner to use a build flag? What does the patch look like*? Can we
instead add something to third_party/libpng/libpngconf.h [1]?

[1] https://skia.googlesource.com/skia/+/master/third_party/libpng/pnglibconf.h

I just answered my own question. It can be found here: [2]. It does the
following:
- Update configure.ac andMakefile.am
  - We don't use either of these, so do we need these changes?
- Modify pngpriv.h
  - Can we instead modify our pnglibconf.h? It looks like pngpriv.h includes it?

[2]
https://skia.googlesource.com/third_party/libpng/+/v1.6.22rc01/contrib/intel/...

[scroggo, 2016/05/16 21:16:09]

Matt said:
:(

My preference would be to update libpng to not require a patch, but I guess we
cannot have that for this version no matter what.

Please document in this file why we're pulling from your repository and what we
need to do to stop (and/or file a bug).

We should also have a README.google describing what our modifications are (and
why). Maybe that belongs in your repository, but perhaps we should also modify
the README we have checked into  third_party/libpng [1].

[1] https://skia.googlesource.com/skia/+/master/third_party/libpng/README.google

   "third_party/externals/giflib"  : "https://android.googlesource.com/platform/external/giflib.git@ab10e256df4f684260ca239905b1cec727181f6c",
 
   "third_party/externals/dng_sdk" : "https://android.googlesource.com/platform/external/dng_sdk.git@96443b262250c390b0caefbf3eed8463ba35ecae",
   "third_party/externals/piex"    : "https://android.googlesource.com/platform/external/piex.git@be908191d0a6883a95333bdc0bca749c9b830969",
 
   "third_party/externals/libjpeg-turbo"             : "https://skia.googlesource.com/third_party/libjpeg-turbo.git@debddedc75850bcdeb8a57258572f48b802a4bb3",
   # libjpeg-turbo depends on yasm to compile .asm files
   "third_party/externals/yasm/source/patched-yasm/" : "https://chromium.googlesource.com/chromium/deps/yasm/patched-yasm.git@4671120cd8558ce62ee8672ebf3eb6f5216f909b",
   "third_party/externals/yasm/binaries"             : "https://chromium.googlesource.com/chromium/deps/yasm/binaries.git@52f9b3f4b0aa06da24ef8b123058bb61ee468881",
 
@@ skipping 26 matching lines @@
     # xSAN bots build Clang from scratch.
     "third_party/externals/llvm": "https://llvm.googlesource.com/llvm@release_38",
     "third_party/externals/llvm/tools/clang": "https://llvm.googlesource.com/clang@release_38",
     "third_party/externals/llvm/projects/compiler-rt": "https://llvm.googlesource.com/compiler-rt@release_38",
     "third_party/externals/llvm/projects/libcxx": "https://llvm.googlesource.com/libcxx@release_38",
     "third_party/externals/llvm/projects/libcxxabi": "https://llvm.googlesource.com/libcxxabi@release_38",
   }
 }
 
 recursedeps = [ "common" ]