Bug 1318283: UpdateFilter can sometimes invalidate the draw target. Back out the previous speculative patch. r=mstange

MozReview-Commit-ID: 8u2sjS9dyLu

--HG--
extra : rebase_source : 876ec3d4d2cd47d76fe57db645764eba281209d9

dom/canvas/CanvasRenderingContext2D.cpp

@@ -1874,10 +1874,9 @@ NS_IMETHODIMP
 CanvasRenderingContext2D::SetDimensions(int32_t aWidth, int32_t aHeight)
 {
   bool retainBuffer = false;
-  // See bug 1318283 as to why we are disabling this optimization.
-  // Based on the results of the investigation, this may go away
-  // completely or come back.
-  // retainBuffer = (aWidth == mWidth && aHeight == mHeight);
+  if (aWidth == mWidth && aHeight == mHeight) {
+    retainBuffer = true;
+  }
   ClearTarget(retainBuffer);
 
   // Zero sized surfaces can cause problems.

dom/canvas/CanvasRenderingContext2D.h

@@ -999,6 +999,7 @@ protected:
     bool isWriteOnly = mCanvasElement && mCanvasElement->IsWriteOnly();
     if (CurrentState().filterSourceGraphicTainted != isWriteOnly) {
       UpdateFilter();
+      EnsureTarget();
     }
     MOZ_ASSERT(CurrentState().filterSourceGraphicTainted == isWriteOnly);
     return CurrentState().filter;