https://build.chromium.org/p/chromium.mac/builders/Mac10.10%20Tests/builds/19246
https://build.chromium.org/p/chromium.mac/builders/Mac10.11%20Tests/builds/13694
https://build.chromium.org/p/chromium.mac/builders/Mac10.12%20Tests/builds/1512

Fairly large number of changes.

From https://chromium-swarm.appspot.com/task?id=36a79e5513dada10&refresh=10&show_raw=1 :

[26/26] benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop.browse:search:google failed unexpectedly 144.5294s:
  [ RUN      ] browse:search:google@{'case': 'browse', 'group': 'search'}
  Traceback (most recent call last):
    File "/b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/story_runner.py", line 90, in _RunStoryAndProcessErrorIfNeeded
      state.RunStory(results)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/page/shared_page_state.py", line 296, in RunStory
      self._current_page.Run(self)
    File "/b/s/w/ir/third_party/catapult/telemetry/telemetry/page/__init__.py", line 112, in Run
      self.RunPageInteractions(action_runner)
    File "/b/s/w/ir/tools/perf/page_sets/system_health/system_health_story.py", line 142, in RunPageInteractions
      self._DidLoadDocument(action_runner)
    File "/b/s/w/ir/tools/perf/page_sets/system_health/browsing_stories.py", line 292, in _DidLoadDocument
      action_runner.ScrollPageToElement(selector=self._SEARCH_PAGE_2_SELECTOR)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/action_runner.py", line 465, in ScrollPageToElement
      speed_in_pixels_per_second=speed_in_pixels_per_second))
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/action_runner.py", line 56, in _RunAction
      action.RunAction(self._tab)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/scroll_to_element.py", line 85, in RunAction
      self._scroller.RunAction(tab)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/scroll.py", line 110, in RunAction
      tab.WaitForJavaScriptCondition('window.__scrollActionDone', timeout=60)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/browser/web_contents.py", line 191, in WaitForJavaScriptCondition
      return self._inspector_backend.WaitForJavaScriptCondition(*args, **kwargs)
    File "/b/s/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/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py", line 293, in WaitForJavaScriptCondition
      e.message + '\n' + debug_message)
  TimeoutException: Timed out while waiting 60s for IsJavaScriptExpressionTrue.
  Console output:
  
  
  [  FAILED  ] browse:search:google@{'case': 'browse', 'group': 'search'} (115879 ms)
  [  PASSED  ] 0 tests.
  [  FAILED  ] 1 test, listed below:
  [  FAILED  ]  browse:search:google@{'case': 'browse', 'group': 'search'}
  
  1 FAILED TEST


CLs that feel like possible culprits, in order of likelihood:

https://codereview.chromium.org/2656903005 (mac-specific and telemetry-related)
https://chromium-review.googlesource.com/527478 (was reverted once already)
https://chromium-review.googlesource.com/529611 (magic gl stuff)

I'll revert the first CL first and see if it helps.