It's flaky at around 1-in-30 runs, but should probably be marked as Flaky.

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest.WebglConformance_conformance_ogles_GL_exp2_exp2_001_to_008&testType=webgl2_conformance_tests

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f2ccb8906079b44ecaabd6b0fb6c683cc0a06624

commit f2ccb8906079b44ecaabd6b0fb6c683cc0a06624
Author: Kenneth Russell <kbr@chromium.org>
Date: Fri Jan 18 01:21:45 2019

Suppress two Mac NVIDIA WebGL conformance flakes.

  conformance/ogles/GL/exp2/exp2_001_to_008.html
  conformance2/textures/canvas/tex-3d-rg16f-rg-float.html

Bug:  922517 , 923080
No-Try: True
Change-Id: Icc604bd2af53b7ac2b447d05b2bd8507e05249fc
Tbr: senorblanco@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/1417839
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623937}
[modify] https://crrev.com/f2ccb8906079b44ecaabd6b0fb6c683cc0a06624/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
[modify] https://crrev.com/f2ccb8906079b44ecaabd6b0fb6c683cc0a06624/content/test/gpu/gpu_tests/webgl_conformance_expectations.py

This one still seems to be failing in the most recent run: https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Release%20%28NVIDIA%29/4799

Not sure why the suppression didn't take.