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

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 160 matching lines @@
     void setAlphaAsFloat(float alpha) { mutableState()->setAlphaAsFloat(alpha);}
     int getNormalizedAlpha() const
     {
         int alpha = immutableState()->alpha();
         return alpha > 255 ? 255 : alpha;
     }
 
     void setImageInterpolationQuality(InterpolationQuality quality) { mutableState()->setInterpolationQuality(quality); }
     InterpolationQuality imageInterpolationQuality() const { return immutableState()->interpolationQuality(); }
 
+    void setCompositeOperation(SkXfermode::Mode);
+    // TODO(dshwang): remove these method. crbug.com/425656
     void setCompositeOperation(CompositeOperator, WebBlendMode = WebBlendModeNormal);
-    CompositeOperator compositeOperation() const { return immutableState()->compositeOperator(); }
-    WebBlendMode blendModeOperation() const { return immutableState()->blendMode(); }
+    CompositeOperator compositeOperation() const;
+    WebBlendMode blendModeOperation() const;
 
     // Specify the device scale factor which may change the way document markers
     // and fonts are rendered.
     void setDeviceScaleFactor(float factor) { m_deviceScaleFactor = factor; }
     float deviceScaleFactor() const { return m_deviceScaleFactor; }
 
     // If true we are (most likely) rendering to a web page and the
     // canvas has been prepared with an opaque background. If false,
     // the canvas may have transparency (as is the case when rendering
     // to a canvas object).
@@ skipping 120 matching lines @@
 
     void drawLineForText(const FloatPoint&, float width, bool printing);
     enum DocumentMarkerLineStyle {
         DocumentMarkerSpellingLineStyle,
         DocumentMarkerGrammarLineStyle
     };
     void drawLineForDocumentMarker(const FloatPoint&, float width, DocumentMarkerLineStyle);
 
     // beginLayer()/endLayer() behaves like save()/restore() for only CTM and clip states.
     void beginTransparencyLayer(float opacity, const FloatRect* = 0);
-    // Apply CompositeOperator when the layer is composited on the backdrop (i.e. endLayer()).
-    // Don't change the current CompositeOperator state.
-    void beginLayer(float opacity, CompositeOperator, const FloatRect* = 0, ColorFilter = ColorFilterNone, ImageFilter* = 0);
+    // Apply SkXfermode::Mode when the layer is composited on the backdrop (i.e. endLayer()).
+    // Don't change the current SkXfermode::Mode states.
+    void beginLayer(float opacity, SkXfermode::Mode, const FloatRect* = 0, ColorFilter = ColorFilterNone, ImageFilter* = 0);
     void endLayer();
 
     // Instead of being dispatched to the active canvas, draw commands following beginRecording()
     // are stored in a display list that can be replayed at a later time. Pass in the bounding
     // rectangle for the content in the list.
     void beginRecording(const FloatRect&, uint32_t = 0);
     PassRefPtr<const SkPicture> endRecording();
 
     bool hasShadow() const;
     void setShadow(const FloatSize& offset, float blur, const Color&,
@@ skipping 186 matching lines @@
     unsigned m_accelerated : 1;
     unsigned m_isCertainlyOpaque : 1;
     unsigned m_printing : 1;
     unsigned m_antialiasHairlineImages : 1;
     unsigned m_shouldSmoothFonts : 1;
 };
 
 } // namespace blink
 
 #endif // GraphicsContext_h