This stores the layer as part of the framebuffer object, instead of the
renderbuffer, and passes it to the renderer at draw time.

Change-Id: I947f8a58ba7a119cc9d890659c99e7e05d0d1d91
Reviewed-on: https://swiftshader-review.googlesource.com/14728Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>