Point libpng at upstream libpng 1.6 + my new perf patch.

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@0.9.35",
   "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@52846504da1f519cf1bb89636caf9110e8677443",
+  #"third_party/externals/libpng"  : "https://skia.googlesource.com/third_party/libpng.git@52846504da1f519cf1bb89636caf9110e8677443",
+  "third_party/externals/libpng"   : "https://github.com/mtklein/libpng.git@0cf9bc11a54a18e6bc34a656b0012580aa05e70b",
   "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@1754202ed3e25b98179a4f377f0bdd605d9a157a",
   "third_party/externals/piex"    : "https://android.googlesource.com/platform/external/piex.git@883a1e5419990f51b8e928969e9c5a09869bce0e",
 
   "third_party/externals/libjpeg-turbo"             : "https://skia.googlesource.com/third_party/libjpeg-turbo.git@b38b934d246fca482eb6801f4ce79422954a635e",
   # 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 11 matching lines @@
   "third_party/externals/icu" : "https://chromium.googlesource.com/chromium/deps/icu.git@ce41627e388fb46ab49671bd16a5db81dcd75a71",
 
   # sdl will be needed for native windows
   "third_party/externals/sdl" : "https://skia.googlesource.com/third_party/sdl@9b526d28cb2d7f0ccff0613c94bb52abc8f53b6f",
 
   # microhttpd for skiaserve
   "third_party/externals/microhttpd" : "https://android.googlesource.com/platform/external/libmicrohttpd@748945ec6f1c67b7efc934ab0808e1d32f2fb98d",
 
   # Mojo SDK for Mojo RPC experiments.
   "third_party/externals/mojo/public" : "https://chromium.googlesource.com/external/github.com/domokit/mojo_sdk@172be18ea745ab29aea132e6cb952e726dc32543",
-  
+
   # shaderc for the vulkan backend
   "third_party/externals/shaderc2" : "https://github.com/google/shaderc.git@d63c5e070fa966a33e1d352b2272bd57e1e9da00",
   "third_party/externals/shaderc2/third_party/googletest" : "https://github.com/google/googletest.git@d225acc90bc3a8c420a9bcd1f033033c1ccd7fe0",
   "third_party/externals/shaderc2/third_party/glslang" : "https://github.com/google/glslang.git@c3869fee412a90c4eadea0bf936ab2530d2dff51",
   "third_party/externals/shaderc2/third_party/spirv-tools" : "https://github.com/KhronosGroup/SPIRV-Tools.git@6836e17f243eebfc4a2950faee49ed3a0015b20b",
 }
 
 deps_os = {
   'llvm': {
     # 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" ]