kbr@ do you know who the right person/team to pass this to is? I actually can't even figure out where this test lives or how to disable it.

Yes, I'll disable the test. It looks like it was previously marked flaky. It's unclear what's happening but the test seems to be intermittently timing out on the Nexus 5X:

https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-marshmallow-arm64-rel/81702
https://chromium-swarm.appspot.com/task?id=3fdc862684195110&refresh=10&show_raw=1

  Traceback (most recent call last):
    File "/b/swarming/w/ir/third_party/catapult/telemetry/telemetry/testing/serially_executed_browser_test_case.py", line 214, in <lambda>
      return lambda self: based_method(self, *args)
    File "/b/swarming/w/ir/content/test/gpu/gpu_tests/gpu_integration_test.py", line 185, in _RunGpuTest
      self.RunActualGpuTest(url, *args)
    File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 186, in RunActualGpuTest
      getattr(self, test_name)(test_path, *args[1:])
    File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 200, in _RunConformanceTest
      self._CheckTestCompletion()
    File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 194, in _CheckTestCompletion
      'webglTestHarness._finished', timeout=self._GetTestTimeout())
    File "/b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
      return func(*args, **kwargs)
    File "/b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/action_runner.py", line 261, in WaitForJavaScriptCondition
      return self._tab.WaitForJavaScriptCondition(*args, **kwargs)
    File "/b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
      return func(*args, **kwargs)
    File "/b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/browser/web_contents.py", line 239, in WaitForJavaScriptCondition
      return self._inspector_backend.WaitForJavaScriptCondition(*args, **kwargs)
    File "/b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
      return func(*args, **kwargs)
    File "/b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py", line 301, in WaitForJavaScriptCondition
      e.message + '\n' + debug_message)
  TimeoutException: 
  Exception thrown when trying to capture console output: TimeoutException('',)

This test was previously marked flaky in  Issue 793050 . I'm not sure why the test would fail 3 times in a row with fresh browser restarts in between, but will mark it failing.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eaef011ff46ce0df26d22e82779eb0096390c664

commit eaef011ff46ce0df26d22e82779eb0096390c664
Author: Kenneth Russell <kbr@chromium.org>
Date: Mon Sep 10 18:07:07 2018

Suppress deqp/data/gles2/shaders/conversions.html on Nexus 5X.

The test recently and unexpectedly became so flaky (timing out) that
it was failing its 3 retries.

Bug:  882323 
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: I79865837adcab6553693cdf3cb37db356a7d3816
No-Try: True
Tbr: ynovikov@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1216085
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589980}
[modify] https://crrev.com/eaef011ff46ce0df26d22e82779eb0096390c664/content/test/gpu/gpu_tests/webgl_conformance_expectations.py

Now that the suppression has landed I'm closing this as WontFix. When we have more recent bots running the WebGL conformance tests we can consider investigating re-enabling this test.