This makes it relatively simple to sample from a D3D11Texture of
arbitrary format.

From: https://bugzilla.mozilla.org/show_bug.cgi?id=1322746

BUG=angleproject:2233
TEST=angle_end2end_tests

Change-Id: I10cd3043b5cb0c5d36dd613467ba6c0ceadf41af
Reviewed-on: https://chromium-review.googlesource.com/758042
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>