Make beginLayer() and CanvasRenderingContext2D use SkXfermode::Mode.

Source/platform/graphics/GraphicsContextState.h

 // Copyright (C) 2013 Google Inc. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 109 matching lines @@
     void setTextDrawingMode(TextDrawingModeFlags mode) { m_textDrawingMode = mode; }
 
     // Common shader state.
     int alpha() const { return m_alpha; }
     void setAlphaAsFloat(float);
 
     SkColorFilter* colorFilter() const { return m_colorFilter.get(); }
     void setColorFilter(PassRefPtr<SkColorFilter>);
 
     // Compositing control, for the CSS and Canvas compositing spec.
-    void setCompositeOperation(CompositeOperator, WebBlendMode);
-    CompositeOperator compositeOperator() const { return m_compositeOperator; }
-    WebBlendMode blendMode() const { return m_blendMode; }
+    void setCompositeOperation(SkXfermode::Mode);
+    SkXfermode::Mode compositeOperation() const { return m_compositeOperation; }
 
     // Image interpolation control.
     InterpolationQuality interpolationQuality() const { return m_interpolationQuality; }
     void setInterpolationQuality(InterpolationQuality);
 
     bool shouldAntialias() const { return m_shouldAntialias; }
     void setShouldAntialias(bool);
 
     bool shouldClampToSourceRect() const { return m_shouldClampToSourceRect; }
     void setShouldClampToSourceRect(bool shouldClampToSourceRect) { m_shouldClampToSourceRect = shouldClampToSourceRect; }
@@ skipping 27 matching lines @@
     RefPtr<Pattern> m_fillPattern;
 
     RefPtr<SkDrawLooper> m_looper;
     RefPtr<SkImageFilter> m_dropShadowImageFilter;
 
     TextDrawingModeFlags m_textDrawingMode;
 
     int m_alpha;
     RefPtr<SkColorFilter> m_colorFilter;
 
-    CompositeOperator m_compositeOperator;
-    WebBlendMode m_blendMode;
+    SkXfermode::Mode m_compositeOperation;
 
     InterpolationQuality m_interpolationQuality;
 
     uint16_t m_saveCount;
 
     bool m_shouldAntialias : 1;
     bool m_shouldClampToSourceRect : 1;
 };
 
 } // namespace blink
 
 #endif // GraphicsContextState_h