This will allow ANGLE to be more conformant when it accepts 32-bit
depth as a Renderbuffer format.

BUG=angleproject:1230

Change-Id: I9336c6f951d280b2332fc3e6d2e640852473aa03
Reviewed-on: https://chromium-review.googlesource.com/313994Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>