Reland r158910 "Improve GIF decoding performance"

Source/web/WebKitUnitTests.isolate

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #         * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #         * Redistributions in binary form must reproduce the above
@@ skipping 19 matching lines @@
 
 {
   'conditions': [
     ['OS=="android"', {
       'variables': {
         'isolate_dependency_tracked': [
         ],
         'isolate_dependency_untracked': [
           'tests/data/',
           # Required by some image decoder tests.
+          '../core/platform/image-decoders/testing/',
           '../../LayoutTests/fast/images/resources/',
         ],
       },
     }],
   ],
 }