Note:
mat_01 reported flaky in issue 636648
mat_02 reported flaky in  issue 644360 
   tmp reported flaky in  issue 659871 

Possibly these all are duplicates.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1e3fb4be7c614a5622408e5f204ab786a70cef3

commit f1e3fb4be7c614a5622408e5f204ab786a70cef3
Author: Yuly Novikov <ynovikov@chromium.org>
Date: Wed Aug 02 01:50:50 2017

Mark a WebGL2 test Flaky

deqp/functional/gles3/shaderindexing/mat_00.html on Mac AMD

BUG= 751254 
TBR=kbr@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I61f545a7f9af55b381affd55959a017c0f92c575
Reviewed-on: https://chromium-review.googlesource.com/596928
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491197}
[modify] https://crrev.com/f1e3fb4be7c614a5622408e5f204ab786a70cef3/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

@ynovikov: Could you please close the issue, if there is no further work to be done.
Thanks!!

There is still hope that someone will investigate this further and fix the actual failure reason.

Going to coalesce multiple reports of the same set of tests into a single bug.