nsIStyleContext* aContext,
nsStyleContext*  aContext,
CanvasFrame::Init(nsIPresContext*  aPresContext,              nsIContent*      aContent,              nsIFrame*        aParent,              nsIStyleContext* aContext,              nsIFrame*        aPrevInFlow){  nsresult rv = nsHTMLContainerFrame::Init(aPresContext,aContent,aParent,aContext,aPrevInFlow);  nsCOMPtr<nsIPresShell> presShell;  aPresContext->GetShell(getter_AddRefs(presShell));  presShell->GetViewManager(getter_AddRefs(mViewManager));  nsIScrollableView* scrollingView = nsnull;  mViewManager->GetRootScrollableView(&scrollingView);  if (scrollingView) {    scrollingView->AddScrollPositionListener(this);  }  return rv;}