sunnyps@ ran into a similar problem in  Issue 859705 . The GPU process was crashing and this crash was being silently swallowed by the harness.

What is the next step here? Is this specific to gpu_tests?

Yes, this is specific to the GPU tests and the WebGL conformance harness in particular:
https://cs.chromium.org/chromium/src/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py?q=webgl_conformance_integra&sq=package:chromium&g=0&l=1

It would be racy, but we could try to confirm at the end of each test that the GPU process is still alive. If not, do something - fail the test and restart the browser?

A volunteer is needed to try this option and see whether it works.

Ran into this again in  bug 878920 . I'm going to try to add crash detection to the harness.

I've discovered that the test harness can retrieve a crash count for the GPU process. All we have to do is check it. https://crrev.com/c/1318834

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8b6d6b499e599f0a23613635a877492e5144b20d

commit 8b6d6b499e599f0a23613635a877492e5144b20d
Author: James Darpinian <jdarpinian@chromium.org>
Date: Tue Nov 06 21:54:49 2018

Fail WebGL tests if GPU process crashes.

Bug:  863221 
Change-Id: Id2fe5975439c2d2cb5ee59c80f7c02a7fce3320d
Reviewed-on: https://chromium-review.googlesource.com/c/1318834
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605835}
[modify] https://crrev.com/8b6d6b499e599f0a23613635a877492e5144b20d/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py