The failure log contains:

10:24:52.786 7035 worker/6 fast/webgl/webgl-composite-modes-repaint.html output stderr lines:
10:24:52.786 7035   Xlib:  extension "RANDR" missing on display ":100".
10:24:52.786 7035   
10:24:52.786 7035   DevTools listening on ws://127.0.0.1:45846/devtools/browser/8ed74498-d6ea-452a-ae39-6b3138c06a87
10:24:52.786 7035   [7042:7287:1204/102446.895428:ERROR:instance.cc(49)] Unable to locate service manifest for metrics
10:24:52.786 7035   [7042:7287:1204/102446.895791:ERROR:service_manager.cc(890)] Failed to resolve service name: metrics
10:24:52.786 7035   [7042:7287:1204/102447.033746:ERROR:instance.cc(49)] Unable to locate service manifest for metrics
10:24:52.786 7035   [7042:7287:1204/102447.033818:ERROR:service_manager.cc(890)] Failed to resolve service name: metrics
10:24:52.786 7035   [7294:7294:1204/102447.559070:WARNING:gpu_info.cc(103)] No active GPU found, returning primary GPU.
10:24:52.786 7035   [7042:7287:1204/102447.565964:ERROR:instance.cc(49)] Unable to locate service manifest for metrics
10:24:52.786 7035   [7042:7287:1204/102447.566037:ERROR:service_manager.cc(890)] Failed to resolve service name: metrics
10:24:52.791 2179 [8/11] fast/webgl/webgl-composite-modes-repaint.html failed unexpectedly (test timed out)
10:24:52.788 7035 worker/6 killing primary driver
10:24:52.791 7035 worker/6 killing secondary driver
10:24:52.791 7035 worker/6 fast/webgl/webgl-composite-modes-repaint.html failed:
10:24:52.791 7035 worker/6  test timed out

Could the failure to look up the metrics service have caused content_shell to time out?

Note: I doubt that's related because there are over 1,000 instances (!) of that error message in this log:

https://chromium-swarm.appspot.com/task?id=3a3b8c96c9b2cf10&refresh=10&show_raw=1

and only three test failures.

Could there be some sort of race condition in the test as it's written?

https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/fast/webgl/webgl-composite-modes-repaint.html?q=webgl-composite-modes-repaint.html&sq=package:chromium&l=1

Is it problematic that it uses onload() and only from in there informs the test harness that it calls testRunner.waitUntilDone()?



Should it just be rewritten with the new testharness.js

To get this out of the sheriff queue, I'm going to assign this; please triage further as needed

(Not disabling test since failures look pretty occasional)

Justin, I'm not that familiar with Blink's test harnesses any more so please tell me if you want me to take this over. But any help or advice you can offer here would be appreciated. I don't know what's legal and not in these tests.

Looking at the flakiness dashboard it seems pretty obvious that this is just a test that takes a long time to run.  We should just mark it as slow rather than flaky.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a230ed80863b3fb23f445e7b130fc0c5a9ee321e

commit a230ed80863b3fb23f445e7b130fc0c5a9ee321e
Author: Justin Novosad <junov@chromium.org>
Date: Wed Dec 13 20:56:13 2017

Mark fast/webgl/webgl-composite-modes-repaint.html as slow

Slow on linux and win

BUG= 791659 
TBR=kbr@chromium.org

Change-Id: I40014560e5aa3b3825fe236bfab65360fda16e13
Reviewed-on: https://chromium-review.googlesource.com/825170
Reviewed-by: Justin Novosad <junov@chromium.org>
Commit-Queue: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523870}
[modify] https://crrev.com/a230ed80863b3fb23f445e7b130fc0c5a9ee321e/third_party/WebKit/LayoutTests/SlowTests

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fa8b12920e8c2042e47816d004b113c155e81aee

commit fa8b12920e8c2042e47816d004b113c155e81aee
Author: Alexis Hetu <sugoi@google.com>
Date: Fri Jul 06 14:14:32 2018

Attempt to unmark some tests as slow/timeout

Now that SwiftShader is on Linux/Windows/MacOS and that a recent
performance improvement has been landed in SwiftShader, verify
which tests still require the Slow/Timeout markers and which don't.

TBR=kbr@chromium.org

Bug:chromium:24182  chromium:433711  chromium:763197  chromium:311482   chromium:243871   chromium:664857   chromium:9798   chromium:237270   chromium:241576   chromium:241869   chromium:246749   chromium:535478   chromium:363029   chromium:364225   chromium:552556   chromium:570656   chromium:584807  chromium:614910  chromium:791659   chromium:726075   chromium:808153  chromium:816045  chromium:693568  chromium:626703 chromium:703533 chromium:786641  chromium:799137   chromium:831686   chromium:831230  chromium:818324  chromium:810437   chromium:847205  chromium:848799  chromium:828962   chromium:849284   chromium:855055 

Change-Id: I5d36d20bd87b234fefe4da3ea7e4af039c0188cb
Reviewed-on: https://chromium-review.googlesource.com/1102341
Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572962}
[modify] https://crrev.com/fa8b12920e8c2042e47816d004b113c155e81aee/third_party/WebKit/LayoutTests/SlowTests
[modify] https://crrev.com/fa8b12920e8c2042e47816d004b113c155e81aee/third_party/WebKit/LayoutTests/TestExpectations