Returns the instance of ILinearGradient or IRectangularGradientassociated with this interior or null if there is no gradient associated with this interior.
Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2