Explicitly disable WebGL2 where D3D11 is disabled.

BUG=706366
TEST=gpu_unittests
R=capn@chromium.org
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

Review-Url: https://codereview.chromium.org/2824833002
Cr-Commit-Position: refs/heads/master@{#465278}
1 file changed