I tried this case 60 times (Ubuntu 16.04), finally got one fail.
How about add one --test-launcher-retry-till-fail flag, case will keep retrying till fail?  This would be helpful for flaky case.

danakj@ shared this script to retry a command till it fails:

#!/bin/bash
COUNTER=0
until [ $? -ne 0 ]; do
    let COUNTER+=1
    echo "fail: attempt #$COUNTER"
    "$@"
done

Usage: fail out/Release/cc_unittests --gtest_filter="LayerTreeHostPictureTestTwinLayer.RunMultiThread_DelegatingRenderer"

Got this here:
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/504173

And here:
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/525826

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/155ed73f14c7b9fa58d366197fe335d06b9d5775

commit 155ed73f14c7b9fa58d366197fe335d06b9d5775
Author: danakj <danakj@chromium.org>
Date: Thu Apr 26 18:33:43 2018

Deflake LayerTreeHostPictureTestTwinLayer test.

The test was doing EndTest() on the main thread after the 5th
DidCommit(), but then verifying the number of /activations/ that
happened, which was incremented on the compositor thread in
DidActivateTreeOnThread(). Since the DidCommit() races with the
DidActivateTreeOnThread(), then number of reported activations
after the test ended could be wrong.

Fix this by moving the EndTest() call to the compositor thread, after
the 5th activation.

R=enne@chromium.org

Bug:  769344 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Id78f72b9a3d7a7a5ae140dcca74e396e72114a2e
Reviewed-on: https://chromium-review.googlesource.com/1028519
Commit-Queue: enne <enne@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554093}
[modify] https://crrev.com/155ed73f14c7b9fa58d366197fe335d06b9d5775/cc/trees/layer_tree_host_unittest_picture.cc