NS_IMETHOD GetPrevInFlow(nsIFrame** aPrevInFlow) const { *aPrevInFlow = mPrevInFlow; return NS_OK;
virtual nsIFrame* GetPrevInFlow() const { return mPrevInFlow;
  NS_IMETHOD GetPrevInFlow(nsIFrame** aPrevInFlow) const {    *aPrevInFlow = mPrevInFlow;    return NS_OK;  }