Added an abstract Renderer::clear method. TRAC #22041 Unimplemented in Renderer11 and Renderer9 only forces the depth stencil state to reset. Signed-off-by: Shannon Woods Signed-off-by: Daniel Koch Author: Geoff Lang git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1423 736b8ea6-26fd-11df-bfd4-992fa37f6226