Fix multisample framebuffer validation ASSERT Change-Id: I1b02ed7209f30549c17f46aeb3726ba1254df3ea Reviewed-on: https://chromium-review.googlesource.com/239270 Tested-by: Austin Kinross <aukinros@microsoft.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>