My guess on root cause:
https://chromium-review.googlesource.com/c/chromium/src/+/1005017
"In order to be able to use SwiftShader on the bots, use_egl must be true
so that the EGL codepath is compiled into the executable."
It happened right before tests got flakey.
This CL already had 2 unexpected failures in the first run.
virtual/gpu-rasterization/images/2-comp.html
virtual/gpu-rasterization/images/cross-fade-svg-fragments.html
The note on the commit says:
""
*** PLEASE DO NOT REVERT THIS CL ***
(unless there's a major issue of course)
If a few layout tests fail or are slow on the bots, please add them to:
third_party/WebKit/LayoutTests/TestExpectations
or
third_party/WebKit/LayoutTests/SlowTests
instead of reverting the entire cl.
"
That sounds like a reasonable guess.
This test also apparently has had a history of flaky failure; it was listed on 2018-02-19 as failure for Mac in TestExpectations, with a line associated with bug 771643 . Although it's possible that the current flaky timeout is related to the change to set use_egl to true.
Note that it's expected that, while switching from OSMesa to SwiftShader fixes many issues, it can introduce some flakiness in some tests at the beginning, but these issues should be ironed out as we fix these one by one. It is perfectly acceptable to add flaky tests to the TestExpectations file, pointing to issue 726075 , and we will try to solve all these issues as soon as possible.
Comment 1 by atotic@chromium.org
, May 21 2018