Showing up on the commit queue at a rate of about once a day, or less frequently. Some recent failures:

https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/221998
https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/220385
https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/219008

Failure mode:

[ RUN      ] WebglConformance.conformance_canvas_drawingbuffer_hd_dpi_test
(INFO) 2016-05-15 16:59:33,430 cache_temperature.EnsurePageCacheTemperature:29  PageCacheTemperature: any
[1380:2492:0515/165933:INFO:CONSOLE(11)] "at (60, 124) expected: 0,255,0,255 was 0,0,0,255", source:  (11)
[1380:2492:0515/165933:INFO:CONSOLE(11)] "FAIL at (60, 124) expected: 0,255,0,255 was 0,0,0,255", source:  (11)
[1380:2492:0515/165933:INFO:CONSOLE(11)] "at (508, 252) expected: 0,255,0,255 was 0,0,0,0", source:  (11)
[1380:2492:0515/165933:INFO:CONSOLE(11)] "FAIL at (508, 252) expected: 0,255,0,255 was 0,0,0,0", source:  (11)
[1380:2492:0515/165934:INFO:CONSOLE(11)] "at (252, 508) expected: 0,255,0,255 was 0,0,0,0", source:  (11)
[1380:2492:0515/165934:INFO:CONSOLE(11)] "FAIL at (252, 508) expected: 0,255,0,255 was 0,0,0,0", source:  (11)
FLAKY TEST FAILURE, retrying: WebglConformance.conformance_canvas_drawingbuffer_hd_dpi_test
FLAKY TEST FAILURE, retrying: WebglConformance.conformance_canvas_drawingbuffer_hd_dpi_test
Traceback (most recent call last):
  File "c:\users\chrome~1\appdata\local\temp\rundyiu7p\third_party\catapult\telemetry\telemetry\internal\story_runner.py", line 84, in _RunStoryAndProcessErrorIfNeeded
    state.RunStory(results)
  File "c:\users\chrome~1\appdata\local\temp\rundyiu7p\content\test\gpu\gpu_tests\gpu_test_base.py", line 122, in RunStory
    RunStoryWithRetries(DesktopGpuSharedPageState, self, results)
  File "c:\users\chrome~1\appdata\local\temp\rundyiu7p\content\test\gpu\gpu_tests\gpu_test_base.py", line 95, in RunStoryWithRetries
    super(cls, shared_page_state).RunStory(results)
  File "c:\users\chrome~1\appdata\local\temp\rundyiu7p\third_party\catapult\telemetry\telemetry\page\shared_page_state.py", line 332, in RunStory
    self._current_page, self._current_tab, results)
  File "c:\users\chrome~1\appdata\local\temp\rundyiu7p\content\test\gpu\gpu_tests\webgl_conformance.py", line 87, in ValidateAndMeasurePage
    raise page_test.Failure(_WebGLTestMessages(tab))
Failure: at (252, 508) expected: 0,255,0,255 was 0,0,0,0
FAIL at (252, 508) expected: 0,255,0,255 was 0,0,0,0


[  FAILED  ] WebglConformance.conformance_canvas_drawingbuffer_hd_dpi_test (792 ms)

It's distressing that the flaky retry mechanism isn't addressing this issue.