Add SkCodec, including PNG implementation.

gyp/libpng.gyp

Index: gyp/libpng.gyp
diff --git a/gyp/libpng.gyp b/gyp/libpng.gyp
index 92ff8d5e77cdf4a6acc98092096af7ef63af4318..7bb0c420915cafadb6043d4681347b346dc27009 100644
--- a/gyp/libpng.gyp
+++ b/gyp/libpng.gyp
@@ -32,10 +32,25 @@
               '-w',
               '-fvisibility=hidden',
             ],
+            'actions': [
+              {
+                'action_name': 'generate_pngconf',
+                'variables' : {
+                  'prebuilt': '../third_party/externals/libpng/scripts/pnglibconf.h.prebuilt',
+                  'generated': '../third_party/externals/libpng/pnglibconf.h',
+                },
+                'inputs': [
+                  '<(prebuilt)',
+                ],
+                'outputs': [
+                  '<(generated)',
+                ],
+                'action': ['cp', '<(prebuilt)', '<(generated)'],
+              },
+            ],
             '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 +60,6 @@
               '../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',