Add an alternate paintContents method to WebContentLayerClient.

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 601 matching lines @@
       'graphics/ImageFrameGenerator.cpp',
       'graphics/ImageFrameGenerator.h',
       'graphics/ImageObserver.cpp',
       'graphics/ImageObserver.h',
       'graphics/ImageOrientation.cpp',
       'graphics/ImageOrientation.h',
       'graphics/ImageSource.cpp',
       'graphics/ImageSource.h',
       'graphics/LoggingCanvas.cpp',
       'graphics/LoggingCanvas.h',
-      'graphics/OpaqueRectTrackingContentLayerDelegate.cpp',
-      'graphics/OpaqueRectTrackingContentLayerDelegate.h',
+      'graphics/ContentLayerDelegate.cpp',
+      'graphics/ContentLayerDelegate.h',
       'graphics/Path.cpp',
       'graphics/Path.h',
       'graphics/PathTraversalState.cpp',
       'graphics/PathTraversalState.h',
       'graphics/Pattern.cpp',
       'graphics/Pattern.h',
       'graphics/ProfilingCanvas.cpp',
       'graphics/ProfilingCanvas.h',
       'graphics/RecordingImageBufferSurface.cpp',
       'graphics/RecordingImageBufferSurface.h',
@@ skipping 315 matching lines @@
     # NOTE: these are legacy unit tests, do not add more!
     'platform_web_unittest_files': [
       'graphics/BitmapImageTest.cpp',
       'graphics/Canvas2DLayerBridgeTest.cpp',
       'graphics/Canvas2DLayerManagerTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/GraphicsLayerTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/ImageLayerChromiumTest.cpp',
-      'graphics/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }