We were allowing calls to the device to check support for D3DFMT_NULL,
which AMD reports as a usable texture type. This was causing crashes
with the WebGL CTS and angle_end2end_tests, when the user tries to use
an sRGB or other type, which we incorrectly reported as available.

BUG=angle:839

Change-Id: I4941baac6a2b14a09c0ad2c924f29189ccfc6a07
Reviewed-on: https://chromium-review.googlesource.com/232728Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>