Add expectations for issue 728670

Broadens webgl2 flaky expectations to video/* and image_bitmap_from_video/*.

Tightens both webgl and webgl2 to d3d11 only (should work).

TBR=kbr@chromium.org
NOTRY=true

Bug: 728670
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I767cbe9925beb519f9a7ad0a3b681e39245a2928
Reviewed-on: https://chromium-review.googlesource.com/526315
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#477407}
2 files changed