This bug only presented itself in our D3D9 Renderer. In D3D11 we
would stretch the texture to fit -- this is behaviour correct in
ES3 but not in the ANGLE spec draft.

BUG=angle:769

Change-Id: Iddb8551c9645aa6f0841e2dc9d96fbd196bc6788
Reviewed-on: https://chromium-review.googlesource.com/221061Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>