Add SkCodec, including PNG implementation.

gyp/libpng.gyp

Index: gyp/libpng.gyp
diff --git a/gyp/libpng.gyp b/gyp/libpng.gyp
index 92ff8d5e77cdf4a6acc98092096af7ef63af4318..1ca6eef25343498577152b422f2c8ebf48c4c573 100644
--- a/gyp/libpng.gyp
+++ b/gyp/libpng.gyp
@@ -16,6 +16,8 @@
             'type': 'static_library',
             'include_dirs': [
               '../third_party/externals/libpng',
+              # Needed for generated pnglibconf.h
+              '../third_party/libpng',
             ],
             'dependencies': [
               'zlib.gyp:zlib',
@@ -26,16 +28,27 @@
             'direct_dependent_settings': {
               'include_dirs': [
                 '../third_party/externals/libpng',
+                # Needed for generated pnglibconf.h
+                '../third_party/libpng',
               ],
             },
             'cflags': [
               '-w',
               '-fvisibility=hidden',
             ],
+            'conditions': [
+              ['not arm_neon', {
+                'defines': [
+                    # FIXME: Why is this needed? Without it, pngpriv.h sets it
+                    # to 2 if __ARM_NEON is defined, but shouldn't __ARM_NEON
+                    # not be defined since arm_neon is 0?
+                    'PNG_ARM_NEON_OPT=0',
+                ],
+              }],
+            ],
             'sources': [
               '../third_party/externals/libpng/png.c',
               '../third_party/externals/libpng/pngerror.c',
-              '../third_party/externals/libpng/pnggccrd.c',
               '../third_party/externals/libpng/pngget.c',
               '../third_party/externals/libpng/pngmem.c',
               '../third_party/externals/libpng/pngpread.c',
@@ -45,7 +58,6 @@
               '../third_party/externals/libpng/pngrutil.c',
               '../third_party/externals/libpng/pngset.c',
               '../third_party/externals/libpng/pngtrans.c',
-              '../third_party/externals/libpng/pngvcrd.c',
               '../third_party/externals/libpng/pngwio.c',
               '../third_party/externals/libpng/pngwrite.c',
               '../third_party/externals/libpng/pngwtran.c',