Is this a new regression? It's quite concerning.

Apologies, I forgot: now that macOS 10.12.2 has fixed the driver bugs affecting this test, we removed it from the tcuSkipList.js in the WebGL conformance suite. That's why it's attempting to run on Mac for the first time.

The Mac AMD bots need to be upgraded to 10.12.2. Issue 679478 is the first bug in which new bots will be deployed with this OS. Blocking this on that one.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1733d120eb79e2d8d49b18892e60ee1297f646f7

commit 1733d120eb79e2d8d49b18892e60ee1297f646f7
Author: zmo <zmo@chromium.org>
Date: Thu Jun 08 23:24:48 2017

Update WebGL2 conformance test expectations for Mac bots.

BUG= 598930 , 617290 , 618464 ,630800, 641149 , 643866 , 645298 , 646182 , 654187 , 663188 ,665197, 665656 , 676848 , 679682 , 679684 , 679686 , 679687 , 679689 , 679690 , 679691 , 680278 , 684903 
TEST=mac bots on GPU FYI waterfall
TBR=kbr@chromium.org,kainino@chromium.org
NOTRY=true
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/2931993002
Cr-Commit-Position: refs/heads/master@{#478121}

[modify] https://crrev.com/1733d120eb79e2d8d49b18892e60ee1297f646f7/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py