mViewportStyleOverflow.mHorizontal = aX; mViewportStyleOverflow.mVertical = aY;
mViewportStyleOverflow = aOverflow;
  void SetViewportOverflowOverride(PRUint8 aX, PRUint8 aY)  {    mViewportStyleOverflow.mHorizontal = aX;    mViewportStyleOverflow.mVertical = aY;  }