void setDevPixelsPerCSSPixel( const CSSToLayoutDeviceScale & aCSSToLayoutDeviceScale)
  {
    mDevPixelsPerCSSPixel = aCSSToLayoutDeviceScale;
  }

  const CSSToLayoutDeviceScale getDevPixelsPerCSSPixel() const
  {
    return mDevPixelsPerCSSPixel;
  }

inside private:

 CSSToLayoutDeviceScale mDevPixelsPerCSSPixel;