pixel_test on ATI GPU on Mac Retina failing on chromium.gpu/Mac Retina Release (AMD)

Builders failed on: 
- Mac Retina Release (AMD): 
  https://build.chromium.org/p/chromium.gpu/builders/Mac%20Retina%20Release%20%28AMD%29

Example:

[1/42] gpu_tests.pixel_integration_test.PixelIntegrationTest.Pixel_2DCanvasWebGL failed unexpectedly 6.1260s:
  See http://chromium-browser-gpu-tests.commondatastorage.googleapis.com/view_test_results.html?d4082a82957cc3522a48b9fc6547afa969990e63_Mac_Retina_Release_AMD__telemetry for this run's test results
  Downloading gs://chromium-gpu-archive/reference-images/Pixel_2DCanvasWebGL_v3_mac_1002_6821_msaa.png to /b/s/w/ittOoh7x/tmpk3nJPI.png
  Uploading /b/s/w/ittOoh7x/tmpWnlH95.png to gs://chromium-browser-gpu-tests/runs/d4082a82957cc3522a48b9fc6547afa969990e63_Mac_Retina_Release_AMD__telemetry/gen/Pixel_2DCanvasWebGL_d4082a82957cc3522a48b9fc6547afa969990e63.png (publicly readable)
  Uploading /b/s/w/ittOoh7x/tmpOX_6ai.png to gs://chromium-browser-gpu-tests/runs/d4082a82957cc3522a48b9fc6547afa969990e63_Mac_Retina_Release_AMD__telemetry/ref/Pixel_2DCanvasWebGL_d4082a82957cc3522a48b9fc6547afa969990e63.png (publicly readable)
  Uploading /b/s/w/ittOoh7x/tmpCceDt1.png to gs://chromium-browser-gpu-tests/runs/d4082a82957cc3522a48b9fc6547afa969990e63_Mac_Retina_Release_AMD__telemetry/diff/Pixel_2DCanvasWebGL_d4082a82957cc3522a48b9fc6547afa969990e63.png (publicly readable)
  
  Traceback (most recent call last):
    _RunGpuTest at content/test/gpu/gpu_tests/gpu_integration_test.py:125
      self.RunActualGpuTest(url, *args)
    RunActualGpuTest at content/test/gpu/gpu_tests/pixel_integration_test.py:179
      self.fail('Reference image did not match captured screen')
    fail at /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/unittest/case.py:412
      raise self.failureException(msg)
  AssertionError: Reference image did not match captured screen
  
  Locals:
    msg : 'Reference image did not match captured screen'