Implementation of 2D canvas context lost/restored events

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 571 matching lines @@
       'graphics/GraphicsLayerDebugInfo.h',
       'graphics/GraphicsLayerClient.h',
       'graphics/GraphicsLayerFactory.h',
       'graphics/GraphicsTypes.cpp',
       'graphics/GraphicsTypes.h',
       'graphics/GraphicsTypes3D.h',
       'graphics/Image.cpp',
       'graphics/Image.h',
       'graphics/ImageBuffer.cpp',
       'graphics/ImageBuffer.h',
+      'graphics/ImageBufferClient.h',
+      'graphics/ImageBufferSurface.cpp',
+      'graphics/ImageBufferSurface.h',
       'graphics/ImageDecodingStore.cpp',
       'graphics/ImageDecodingStore.h',
       'graphics/ImageFrameGenerator.cpp',
       'graphics/ImageFrameGenerator.h',
-      'graphics/ImageBufferSurface.cpp',
-      'graphics/ImageBufferSurface.h',
       'graphics/ImageObserver.cpp',
       'graphics/ImageObserver.h',
       'graphics/ImageOrientation.cpp',
       'graphics/ImageOrientation.h',
       'graphics/ImageSource.cpp',
       'graphics/ImageSource.h',
       'graphics/LazyDecodingPixelRef.cpp',
       'graphics/LazyDecodingPixelRef.h',
       'graphics/OpaqueRectTrackingContentLayerDelegate.cpp',
       'graphics/OpaqueRectTrackingContentLayerDelegate.h',
@@ skipping 308 matching lines @@
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/gpu/DrawingBufferTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
     ],
   },
 }