Fixing 2D canvas invalidation region tracking.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 829cdb8fb66916bdd22a5e9a786b74057c50b9d2..5e5b8cb970095f11b415d5f6658a9e67b6360461 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -1745,14 +1745,6 @@ void CanvasRenderingContext2D::didDraw(const FloatRect& dirtyRect)
     if (dirtyRect.isEmpty())
         return;
 
-    // If we are drawing to hardware and we have a composited layer, just invalidate layer.
-    if (isAccelerated() && platformLayer()) {

[Stephen White, 2014/07/17 15:28:19]

Can we get rid of the platformLayer() override now? It looks like this might be
the only use.

[Justin Novosad, 2014/07/17 17:07:21]

We can't. That method is a virtual override from CanvasRenderingContext and is
invoked by CompositedLayerMapping.

-        platformLayer()->invalidateRect(dirtyRect);
-        canvas()->clearCopiedImage();
-        canvas()->notifyObserversCanvasChanged(dirtyRect);
-        return;
-    }
-
     canvas()->didDraw(dirtyRect);
 }