Make CanvasRenderingContext2D use SkCanvas directly

Source/platform/graphics/ImageBuffer.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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
@@ skipping 77 matching lines @@
     m_surface->setImageBuffer(this);
 }
 
 ImageBuffer::~ImageBuffer()
 {
 }
 
 GraphicsContext* ImageBuffer::context() const
 {
     if (!isSurfaceValid())
-        return 0;
+        return nullptr;
     ASSERT(m_context.get());
     return m_context.get();
 }
 
+SkCanvas* ImageBuffer::canvas() const
+{
+    if (!isSurfaceValid())
+        return nullptr;
+    return m_surface->canvas();
+}
+
 const SkBitmap& ImageBuffer::bitmap() const
 {
     return m_surface->bitmap();
 }
 
 bool ImageBuffer::isSurfaceValid() const
 {
     return m_surface->isValid();
 }
 
@@ skipping 287 matching lines @@
     ASSERT(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
     Vector<char> encodedImage;
     if (!encodeImage(*this, mimeType, quality, &encodedImage))
         return "data:,";
 
     return "data:" + mimeType + ";base64," + base64Encode(encodedImage);
 }
 
 } // namespace blink