This default format mapping serves as a base for a Renderer format
mapping. Any formats that require emulation or other representation
in a Renderer can be overridden in the renderer layer.

BUG=angleproject:1455

Change-Id: I47f070c2ea132bada9cc0fc4353b89b74b8ee8f3
Reviewed-on: https://chromium-review.googlesource.com/367692Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>