Use SkXfermode::Mode in code related to Image.

Source/platform/graphics/GradientGeneratedImage.h

 /*
  * Copyright (C) 2008, 2012 Apple Computer, 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 30 matching lines @@
     {
         return adoptRef(new GradientGeneratedImage(generator, size));
     }
 
     virtual ~GradientGeneratedImage()
     {
     }
 
 protected:
     void draw(GraphicsContext*, const FloatRect&, const FloatRect&,
-        CompositeOperator, WebBlendMode, RespectImageOrientationEnum) override;
+        SkXfermode::Mode, RespectImageOrientationEnum) override;
     virtual void drawTile(GraphicsContext*, const FloatRect&) final;
 
     GradientGeneratedImage(PassRefPtr<Gradient> generator, const IntSize& size)
         : GeneratedImage(size)
         , m_gradient(generator)
     {
     }
 
     RefPtr<Gradient> m_gradient;
 };
 
 } // namespace blink
 
 #endif