Make UnacceleratedBufferSurface use a SkSurface instead of a SkCanvas

Source/platform/graphics/UnacceleratedImageBufferSurface.h

Index: Source/platform/graphics/UnacceleratedImageBufferSurface.h
diff --git a/Source/platform/graphics/UnacceleratedImageBufferSurface.h b/Source/platform/graphics/UnacceleratedImageBufferSurface.h
index 407cdcbf31149beae3708c49d2048b569b1d86b1..afde20cb0ecb7f20a8a9f4363054dfff95ecc936 100644
--- a/Source/platform/graphics/UnacceleratedImageBufferSurface.h
+++ b/Source/platform/graphics/UnacceleratedImageBufferSurface.h
@@ -34,19 +34,21 @@
 #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