Noticed it flaking here:
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_optional_gpu_tests_rel/1228

[62/138] gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest.WebglConformance_conformance2_transform_feedback_too_small_buffers failed unexpectedly 6.0451s:
  
  Traceback (most recent call last):
    _RunGpuTest at content/test/gpu/gpu_tests/gpu_integration_test.py:132
      self.RunActualGpuTest(url, *args)
    RunActualGpuTest at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:204
      getattr(self, test_name)(test_path, *args[1:])
    _RunConformanceTest at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:218
      self._CheckTestCompletion()
    _CheckTestCompletion at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:214
      self.fail(self._WebGLTestMessages(self.tab))
    fail at .swarming_module/lib/python2.7/unittest/case.py:410
      raise self.failureException(msg)
  AssertionError: buffer should match expected values
  FAIL buffer should match expected values

Will update expectations

Thanks, this one uncovered a lot of bugs. I'm working through all of them now and will hopefully have things de-flaked in the next few days.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6bb2d8a58c8f79e93ad5e9da1abc7cf4ac45efc9

commit 6bb2d8a58c8f79e93ad5e9da1abc7cf4ac45efc9
Author: Yuly Novikov <ynovikov@chromium.org>
Date: Wed Apr 11 05:39:51 2018

Update WebGL2 CTS expectations

conformance2/transform_feedback/too-small-buffers.html
is also flaky on non-passthrough Linux NVIDIA

BUG= 818383 
TBR=kbr@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I73df9ae3b32d253251820b5495e8c77fa01af8f9
Reviewed-on: https://chromium-review.googlesource.com/1006363
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549777}
[modify] https://crrev.com/6bb2d8a58c8f79e93ad5e9da1abc7cf4ac45efc9/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d400565ddce087a38f25df0cfd023a3f93cb7d38

commit d400565ddce087a38f25df0cfd023a3f93cb7d38
Author: James Darpinian <jdarpinian@chromium.org>
Date: Thu Apr 12 05:38:07 2018

Transform feedback fixes are in, remove test failure expectations.

Bug:  696345 , 818383 , 820639 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Iaacb3bbaf738e994ea6caaad7b83c5a8bbf8e964
Reviewed-on: https://chromium-review.googlesource.com/993393
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550025}
[modify] https://crrev.com/d400565ddce087a38f25df0cfd023a3f93cb7d38/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bac7b5cc6ca384e48ec88b1286960c80283e3288

commit bac7b5cc6ca384e48ec88b1286960c80283e3288
Author: Jamie Madill <jmadill@chromium.org>
Date: Thu Apr 12 17:53:38 2018

Suppress two flaky XFB tests on ANGLE/GL.

The failure expectations are restored for two of the three new
tests. Marking as flaky - if they continue to fail despite the
flaky suppression we will need to mark them as failing.

Bug:  696345 
Bug:  818383 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I8ac5db7e2c75f2c50cbea42523767336e5c431ea
Tbr: geofflang@chromium.org
Tbr: jdarpinian@chromium.org
Tbr: kbr@chromium.org
No-try: True
Reviewed-on: https://chromium-review.googlesource.com/1010770
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550263}
[modify] https://crrev.com/bac7b5cc6ca384e48ec88b1286960c80283e3288/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

Remaining test failures will be debugged in bug 832238.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bac7b5cc6ca384e48ec88b1286960c80283e3288

commit bac7b5cc6ca384e48ec88b1286960c80283e3288
Author: Jamie Madill <jmadill@chromium.org>
Date: Thu Apr 12 17:53:38 2018

Suppress two flaky XFB tests on ANGLE/GL.

The failure expectations are restored for two of the three new
tests. Marking as flaky - if they continue to fail despite the
flaky suppression we will need to mark them as failing.

Bug:  696345 
Bug:  818383 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I8ac5db7e2c75f2c50cbea42523767336e5c431ea
Tbr: geofflang@chromium.org
Tbr: jdarpinian@chromium.org
Tbr: kbr@chromium.org
No-try: True
Reviewed-on: https://chromium-review.googlesource.com/1010770
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550263}
[modify] https://crrev.com/bac7b5cc6ca384e48ec88b1286960c80283e3288/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py