Use SkImage as a backing store for copying 2d Contexts to ImageBitmaps.

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 2781 matching lines @@
             'platform/graphics/ImageSource.cpp',
             'platform/graphics/InbandTextTrackPrivate.h',
             'platform/graphics/InbandTextTrackPrivateClient.h',
             'platform/graphics/Latin1TextIterator.h',
             'platform/graphics/MediaPlayer.cpp',
             'platform/graphics/MediaPlayer.h',
             'platform/graphics/Path.cpp',
             'platform/graphics/PathTraversalState.cpp',
             'platform/graphics/PathTraversalState.h',
             'platform/graphics/Pattern.cpp',
+            'platform/graphics/ReadOnlyBitmapImage.cpp',
+            'platform/graphics/ReadOnlyBitmapImage.h',
             'platform/graphics/RoundedRect.cpp',
             'platform/graphics/SegmentedFontData.cpp',
             'platform/graphics/SegmentedFontData.h',
             'platform/graphics/ShadowBlur.cpp',
             'platform/graphics/ShadowBlur.h',
             'platform/graphics/SimpleFontData.cpp',
             'platform/graphics/SVGGlyph.cpp',
             'platform/graphics/StringTruncator.cpp',
             'platform/graphics/StrokeData.cpp',
             'platform/graphics/SurrogatePairAwareTextIterator.cpp',
@@ skipping 993 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++"'
               }],
          ],
     }
 }