Implementation of 2D canvas context lost/restored events

Source/core/html/HTMLCanvasElement.h

Index: Source/core/html/HTMLCanvasElement.h
diff --git a/Source/core/html/HTMLCanvasElement.h b/Source/core/html/HTMLCanvasElement.h
index fa8c45a47d6ccb08159bd6df9a23cfbd02b31988..eb52f06dd4cd8ffa9ea719ca1c980d9af64b93c0 100644
--- a/Source/core/html/HTMLCanvasElement.h
+++ b/Source/core/html/HTMLCanvasElement.h
@@ -34,6 +34,7 @@
 #include "platform/geometry/IntSize.h"
 #include "platform/graphics/Canvas2DLayerBridge.h"
 #include "platform/graphics/GraphicsTypes.h"
+#include "platform/graphics/ImageBufferClient.h"
 #include "wtf/Forward.h"
 
 #define CanvasDefaultInterpolationQuality InterpolationLow
@@ -61,7 +62,7 @@ public:
     virtual void canvasDestroyed(HTMLCanvasElement*) = 0;
 };
 
-class HTMLCanvasElement FINAL : public HTMLElement, public DocumentVisibilityObserver, public CanvasImageSource {
+class HTMLCanvasElement FINAL : public HTMLElement, public DocumentVisibilityObserver, public CanvasImageSource, public ImageBufferClient {
 public:
     static PassRefPtr<HTMLCanvasElement> create(Document&);
     virtual ~HTMLCanvasElement();
@@ -124,7 +125,9 @@ public:
 
     bool is3D() const;
 
-    bool hasImageBuffer() const { return m_imageBuffer.get(); }
+    bool hasImageBuffer() const { return m_imageBuffer; }
+    bool hasValidImageBuffer() const;
+    void discardImageBuffer();
 
     bool shouldAccelerate(const IntSize&) const;
 
@@ -138,6 +141,9 @@ public:
     virtual bool wouldTaintOrigin(SecurityOrigin*) const OVERRIDE;
     virtual FloatSize sourceSize() const OVERRIDE;
 
+    // ImageBufferClient implementation
+    virtual void notifySurfaceInvalid() OVERRIDE;
+
 protected:
     virtual void didMoveToNewDocument(Document& oldDocument) OVERRIDE;
 
@@ -152,8 +158,8 @@ private:
 
     PassOwnPtr<ImageBufferSurface> createImageBufferSurface(const IntSize& deviceSize, int* msaaSampleCount);
     void createImageBuffer();
+    void createImageBufferInternal();
     void clearImageBuffer();
-    void discardImageBuffer();
 
     void setSurfaceSize(const IntSize&);