In this WebGL conformance roll:
https://codereview.chromium.org/2798083005/

WebglConformance_conformance2_textures_canvas_sub_rectangle_tex_2d_rgb16f_rgb_half_float failed reliably:
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_optional_gpu_tests_rel/builds/7546
https://chromium-swarm.appspot.com/task?id=3560121a77996b10&refresh=10&show_raw=1

[13/177] gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest.WebglConformance_conformance2_textures_canvas_sub_rectangle_tex_2d_rgb16f_rgb_half_float failed unexpectedly 8.2114s:
  
  Traceback (most recent call last):
    _RunGpuTest at content/test/gpu/gpu_tests/gpu_integration_test.py:73
      self.RunActualGpuTest(url, *args)
    RunActualGpuTest at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:203
      getattr(self, test_name)(test_path, *args[1:])
    _RunConformanceTest at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:217
      self._CheckTestCompletion()
    _CheckTestCompletion at content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:213
      self.fail(self._WebGLTestMessages(self.tab))
    fail at /usr/lib/python2.7/unittest/case.py:412
      raise self.failureException(msg)
  AssertionError: should be 255,0,0
  at (0, 0) expected: 255,0,0 was 0,0,0
  FAIL should be 255,0,0
  at (0, 0) expected: 255,0,0 was 0,0,0
  should be 255,0,0
...

I wonder whether this might be caused by the recent enabling of EXT_color_buffer_half_float in Chrome's rendering pipeline and/or updates to CopyTextureCHROMIUM.