Refactor Renderer11::getRenderTargetResource to accept a gl::Renderbuffer instead of a gl::Framebuffer.

TRAC #22656

Signed-off-by: Nicolas Capens
Signed-off-by: Shannon Woods
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@2016 736b8ea6-26fd-11df-bfd4-992fa37f6226