WARP does not support surface sharing like native D3D11. This,
combined with a Chromium-side change, should fix WARP rendering
in Chrome.

BUG=angleproject:973
BUG=429792

Change-Id: I41e778625e8697e45657843f2f337bcffe7ddbe2
Reviewed-on: https://chromium-review.googlesource.com/265611Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>