2D canvas: remain in deferred rendering mode with canvas to canvas drawImage

Source/platform/graphics/ImageBuffer.h

Index: Source/platform/graphics/ImageBuffer.h
diff --git a/Source/platform/graphics/ImageBuffer.h b/Source/platform/graphics/ImageBuffer.h
index 6468bde505f9977f8aea21c12b4406e0d5463d76..1d26d9e083a200fffdb232c51eef02694a98d3d9 100644
--- a/Source/platform/graphics/ImageBuffer.h
+++ b/Source/platform/graphics/ImageBuffer.h
@@ -82,7 +82,8 @@ public:
     bool isExpensiveToPaint() const { return m_surface->isExpensiveToPaint(); }
     bool isSurfaceValid() const;
     bool restoreSurface() const;
-    void didDraw(const FloatRect& rect) const { m_surface->didDraw(rect); }
+    void didDraw(const FloatRect&) const;
+    bool wasDrawnToAfterSnapshot() const { return m_snapshotState == DrawnToAfterSnapshot; }
 
     void setFilterQuality(SkFilterQuality filterQuality) { m_surface->setFilterQuality(filterQuality); }
     void setIsHidden(bool hidden) { m_surface->setIsHidden(hidden); }
@@ -138,6 +139,12 @@ public:
 private:
     ImageBuffer(PassOwnPtr<ImageBufferSurface>);
 
+    enum SnapshotState {
+        InitialSnapshotState,
+        DidAcquireSnapshot,
+        DrawnToAfterSnapshot,
+    };
+    mutable SnapshotState m_snapshotState;
     OwnPtr<ImageBufferSurface> m_surface;
     ImageBufferClient* m_client;
 };