Add SkEncodedFormat, used by SkCodec.

gyp/images.gyp

 # GYP file for images project.
 {
   'targets': [
     {
       'target_name': 'images',
       'product_name': 'skia_images',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:*',
         'libjpeg.gyp:*',
         'etc1.gyp:libetc1',
         'ktx.gyp:libSkKTX',
         'libwebp.gyp:libwebp',
         'utils.gyp:utils',
       ],
       'include_dirs': [
+        '../include/core',
         '../include/images',
         '../src/lazy',
         # for access to SkErrorInternals.h
         '../src/core/',
         # for access to SkImagePriv.h
         '../src/image/',
       ],
       'sources': [
         '../include/images/SkDecodingImageGenerator.h',
         '../include/images/SkForceLinking.h',
@@ skipping 135 matching lines @@
         }],
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../include/images',
         ],
       },
     },
   ],
 }