Move overdraw tracking code from GraphicsContext to CanvasRenderingContext2D

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 484 matching lines @@
       'graphics/FrameData.h',
       'graphics/GeneratedImage.cpp',
       'graphics/GeneratedImage.h',
       'graphics/Gradient.cpp',
       'graphics/Gradient.h',
       'graphics/GradientGeneratedImage.cpp',
       'graphics/GradientGeneratedImage.h',
       'graphics/GraphicsContext.cpp',
       'graphics/GraphicsContext.h',
       'graphics/GraphicsContextAnnotation.h',
-      'graphics/GraphicsContextClient.cpp',
-      'graphics/GraphicsContextClient.h',
       'graphics/GraphicsContextState.cpp',
       'graphics/GraphicsContextState.h',
       'graphics/GraphicsContextStateSaver.h',
       'graphics/GraphicsLayer.cpp',
       'graphics/GraphicsLayer.h',
       'graphics/GraphicsLayerClient.h',
       'graphics/GraphicsLayerDebugInfo.cpp',
       'graphics/GraphicsLayerDebugInfo.h',
       'graphics/GraphicsLayerFactory.h',
       'graphics/GraphicsTypes.cpp',
@@ skipping 473 matching lines @@
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/bmp/BMPImageDecoderTest.cpp',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }