Add a fast path for single render target masked clears in Renderer11. TRAC #22898 Signed-off-by: Geoff Lang Signed-off-by: Shannon Woods Author: Jamie Madill git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2265 736b8ea6-26fd-11df-bfd4-992fa37f6226