deqp/functional/gles3/fbomultisample.8_samples.html fails on some ARM devices

Per http://crbug.com/1218509 , deqp/functional/gles3/fbomultisample.8_samples.html fails on some ARM devices in this way:

```
Unexpected exception while running deqp/functional/gles3/fbomultisample.8_samples.html
Traceback (most recent call last):
File "/b/swarming/w/ir/content/test/gpu/gpu_tests/gpu_integration_test.py", line 273, in _RunGpuTest
self.RunActualGpuTest(url, *args)
File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 233, in RunActualGpuTest
getattr(self, test_name)(test_path, test_args)
File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 313, in _RunConformanceTest
self._CheckTestCompletion()
File "/b/swarming/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py", line 309, in _CheckTestCompletion
self.fail(self._WebGLTestMessages(self.tab))
File "/b/swarming/w/ir/.task_template_packages/cpython/lib/python2.7/unittest/case.py", line 410, in fail
raise self.failureException(msg)
AssertionError: msaa.8_samples.r11f_g11f_b10f: Sample count not supported
```

The test may need to better query for the sample counts supported by various internal formats.

Start with deqp/functional/gles3/fbomultisample.8_samples.html and the failure reported from gpu_tests/webgl_conformance_integration_test.py. Reproduce the ARM-device failure and inspect how sample counts are handled for msaa.8_samples.r11f_g11f_b10f; done means the conformance test no longer rejects formats with unsupported sample counts.

Written by the indexing model from the issue text.