Suppress WebGL 2.0 dEQP shaderindexing/varying flake.

Seen flaky on Mac/AMD.

Bug: 928989
Change-Id: I14b72acfd05867caede48d5c37beeb5cb156df5d
Tbr: enne@chromium.org
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/1455654
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629442}
1 file changed