Passed several GPU.FYI bots builds after the builder was brought back to life.
So, only happens on mac_angle_rel_ng so far.
Maybe something wrong with gsutil authentication on it?

I see here:
https://build.chromium.org/p/tryserver.chromium.angle/builders/mac_angle_rel_ng/builds/2996

Pixel_CSSFilterEffects (gpu_tests.pixel_integration_test.PixelIntegrationTest) ... [20956:100111:1220/162945.263714:WARNING:simple_synchronous_entry.cc(1054)] Could not open platform files for entry.
[20956:1295:1220/162945.286623:INFO:CONSOLE(144)] "'webkitRequestAnimationFrame' is vendor-specific. Please use the standard 'requestAnimationFrame' instead.", source: http://127.0.0.1:58854/filter_effects.html (144)
[20956:1295:1220/162945.289003:INFO:CONSOLE(94)] "Uncaught ReferenceError: main is not defined", source: http://127.0.0.1:58854/filter_effects.html (94)
(INFO) 2016-12-20 16:29:52,790 cloud_storage._GetLocked:274  Downloading gs://chromium-gpu-archive/reference-images/Pixel_CSSFilterEffects_v4_mac_10de_0fe9_msaa.png to /b/s/w/itdAsZmR/tmpC792J7.png

Traceback (most recent call last):
  _RunGpuTest at content/test/gpu/gpu_tests/gpu_integration_test.py:78
    self.RunActualGpuTest(url, *args)
  RunActualGpuTest at content/test/gpu/gpu_tests/pixel_integration_test.py:177
    self.fail('Could not find image %s in cloud storage' % image_name)
  fail at /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/unittest/case.py:412
    raise self.failureException(msg)
AssertionError: Could not find image Pixel_CSSFilterEffects in cloud storage

Locals:
  msg : 'Could not find image Pixel_CSSFilterEffects in cloud storage'

But, when I gsutil ls gs://chromium-gpu-archive/reference-images/Pixel_CSSFilterEffects_v4_mac_10de_0fe9_msaa.png from my workstation, the file is there.

I don't understand how mac_angle_rel_ng could be failing but the waterfall bots could be green:

https://build.chromium.org/p/chromium.gpu.fyi/builders/Mac%20Retina%20Release
https://build.chromium.org/p/chromium.gpu.fyi/builders/Mac%20Retina%20Debug

They use the same physical hardware, which is all in Swarming.

Could one of the bots have lost its credentials?

It looks like it was build155-b4 and that in fact it did lose its cloud storage credentials for some time. Here are two failing builds and their Swarming tasks:

https://build.chromium.org/p/tryserver.chromium.angle/builders/mac_angle_rel_ng/builds/2996
https://chromium-swarm.appspot.com/task?id=33378d6b6d220b10&refresh=10&show_raw=1

https://build.chromium.org/p/tryserver.chromium.angle/builders/mac_angle_rel_ng/builds/2993/
https://chromium-swarm.appspot.com/task?id=33371defd7e32610&refresh=10&show_raw=1

Both ran on build155-b4.

This bot's since run pixel_tests successfully:

https://chromium-swarm.appspot.com/bot?id=build155-b4&sort_stats=total%3Adesc

so I assume that the normal reboot cycle replaced the .boto and that it's fixed now.

Please reopen if this is seen again on https://build.chromium.org/p/tryserver.chromium.angle/builders/mac_angle_rel_ng .