Make UnacceleratedBufferSurface use a SkSurface instead of a SkCanvas

Source/platform/graphics/UnacceleratedImageBufferSurface.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
@@ skipping 16 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef UnacceleratedImageBufferSurface_h
 #define UnacceleratedImageBufferSurface_h
 
 #include "platform/graphics/ImageBufferSurface.h"
 #include "wtf/RefPtr.h"
 
+class SkSurface;
+
 namespace WebCore {
 
 class PLATFORM_EXPORT UnacceleratedImageBufferSurface : public ImageBufferSurface {
     WTF_MAKE_NONCOPYABLE(UnacceleratedImageBufferSurface); WTF_MAKE_FAST_ALLOCATED;
 public:
     UnacceleratedImageBufferSurface(const IntSize&, OpacityMode = NonOpaque);
-    virtual ~UnacceleratedImageBufferSurface() { }
+    virtual ~UnacceleratedImageBufferSurface();
 
-    virtual SkCanvas* canvas() const OVERRIDE { return m_canvas.get(); }
-    virtual bool isValid() const OVERRIDE { return m_canvas; }
+    virtual SkCanvas* canvas() const OVERRIDE;
+    virtual bool isValid() const OVERRIDE;
 
 private:
-    RefPtr<SkCanvas> m_canvas;
+    RefPtr<SkSurface> m_surface;
 };
 
 } // namespace WebCore
 
 #endif