Refactoring Canvas2DLayerBridge to make it easier to write unit tests

Source/core/core.gypi

 {
     'variables': {
         'deprecated_perl_core_idl_files': [
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSHostRule.idl',
             'css/CSSImportRule.idl',
             'css/CSSMediaRule.idl',
@@ skipping 3736 matching lines @@
             'loader/cache/MemoryCacheTest.cpp',
             'loader/cache/ResourceFetcherTest.cpp',
             'platform/DecimalTest.cpp',
             'platform/SharedBufferTest.cpp',
             'platform/chromium/ClipboardChromiumTest.cpp',
             'platform/graphics/FontTest.cpp',
             'platform/graphics/GraphicsContextTest.cpp',
             'platform/graphics/UnitBezierTest.cpp',
             'platform/graphics/chromium/AnimationTranslationUtilTest.cpp',
             'platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp',
+            'platform/graphics/chromium/Canvas2DLayerBridgeTestHelper.h',
             'platform/graphics/chromium/Canvas2DLayerManagerTest.cpp',
             'platform/graphics/chromium/DeferredImageDecoderTest.cpp',
             'platform/graphics/chromium/ImageDecodingStoreTest.cpp',
             'platform/graphics/chromium/ImageFrameGeneratorTest.cpp',
             'platform/graphics/chromium/ThreadSafeDataTransportTest.cpp',
             'platform/graphics/chromium/test/MockDiscardablePixelRef.h',
             'platform/graphics/chromium/test/MockImageDecoder.h',
             'platform/graphics/gpu/DrawingBufferTest.cpp',
             'platform/image-decoders/ImageDecoderTest.cpp',
             'platform/image-decoders/gif/GIFImageDecoderTest.cpp',
@@ skipping 35 matching lines @@
                 'bison_exe': 'bison',
                 # We specify a preprocess so it happens locally and won't get
                 # distributed to goma.
                 # FIXME: /usr/bin/gcc won't exist on OSX forever. We want to
                 # use /usr/bin/clang once we require Xcode 4.x.
                 'preprocessor': '--preprocessor "/usr/bin/gcc -E -P -x c++"'
               }],
          ],
     }
 }