Bug 1042772. offsetToReferenceFrame is always zero when we use it. Remove it. r=mattwoodrow

layout/generic/nsFrame.cpp

@@ -1922,8 +1922,6 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
   AutoSaveRestoreBlendMode autoRestoreBlendMode(*aBuilder);
   aBuilder->SetContainsBlendModes(BlendModeSet());
  
-  nsPoint offsetToReferenceFrame = aBuilder->ToReferenceFrame(this);
-
   if (isTransformed) {
     const nsRect overflow = GetVisualOverflowRectRelativeToSelf();
     if (aBuilder->IsForPainting() &&
@@ -1934,10 +1932,9 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
         return;
       }
 
-      dirtyRect += offsetToReferenceFrame;
       nsRect untransformedDirtyRect;
       if (nsDisplayTransform::UntransformRect(dirtyRect, overflow, this,
-            offsetToReferenceFrame, &untransformedDirtyRect)) {
+            nsPoint(0,0), &untransformedDirtyRect)) {
         dirtyRect = untransformedDirtyRect;
       } else {
         NS_WARNING("Unable to untransform dirty rect!");