While these should be supported on ES drivers, ANGLE's texture format
caps generation does not correctly differentiate between renderbuffer
and framebuffer attachment formats and leads to assertion failures.

BUG=779346
BUG=angleproject:1523

Change-Id: I9a49abdf52ae8b1ef91f88a4434ff8c3f95b025b
Reviewed-on: https://chromium-review.googlesource.com/748888Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>