Apparently, this test was marked as flaky in issue 658305:
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/TestExpectations?q=effect-reference-subregion-hw.html&sq=package:chromium&l=1101&dr=C

Nonetheless, it is shown as "Unexpected failure". How is this possible?

Adding folks from the other bug who might know.

The results it says "Timed out", which isn't the same as "Failure" (not yet at least) IIRC. (Maybe it can hit the timeout if rendering takes too long??)

Based on:

  https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=css3%2Ffilters%2Feffect-reference

it appears a lot of these tests are "slow" and occasionally time out. They should probably be cut down a bit. (I.e this particular test applies 14 different filter chains, so probably requires quite a bit of shader compilation and whatnot.)

And, FWIW, issue 658305 has nothing to do with "shader compilation and whatnot" being slow, so there really no relation. If anyone feels like splitting the tests feel free to grab this, because I'm definitely not going to jump on this immediately.

Thanks for adding details.
This test wouldn't be the first one in this group receiving the Timeout label.

Alexis, could this be due to the SwiftShader layout tests switch?

Splitting up the test might not be a bad idea.

Thanks for the quick reaction. Removing sheriff labels for now as this will be marked as timeout with https://crrev.com/c/712714.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f5df9c50a89feb7769b5847d8fa81e1c4e9ffbb8

commit f5df9c50a89feb7769b5847d8fa81e1c4e9ffbb8
Author: Friedrich Horschig <fhorschig@chromium.org>
Date: Wed Oct 11 14:43:46 2017

Mark css3/filters/effect-reference-subregion-hw.html as Timeout

This flaky test is starting to fail due to timeouts. Accept this until
the underlying issue (i.e. shader logic) is fixed.

TBR=yhirano@chromium.org, fs@opera.com

Bug: 773648, 658305
Change-Id: Ibb248836d068f5c1b38a5a312aa9f64836c537f5
Reviewed-on: https://chromium-review.googlesource.com/712714
Commit-Queue: Friedrich Horschig <fhorschig@chromium.org>
Reviewed-by: Friedrich Horschig <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507980}
[modify] https://crrev.com/f5df9c50a89feb7769b5847d8fa81e1c4e9ffbb8/third_party/WebKit/LayoutTests/TestExpectations

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0c6213902cc35b2c9c954bafdf61a844a94cbe8c

commit 0c6213902cc35b2c9c954bafdf61a844a94cbe8c
Author: Reilly Grant <reillyg@chromium.org>
Date: Tue Oct 17 23:05:50 2017

Mark css3/filters/effect-reference-subregion-hw.html as Timeout

This flaky test is starting to fail due to timeouts. Accept this until
the underlying issue (i.e. shader logic) is fixed.

The original change (r507980) attempting to mark this test as Timeout
accidentally changed the line for
css3/filters/effect-reference-subregion.html instead.

TBR=yhirano@chromium.org, fs@opera.com
NOTRY=true

Bug: 773648, 658305
Change-Id: Ie52945d5158037e600ac24a04533d6d0efaecec9
Reviewed-on: https://chromium-review.googlesource.com/724224
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509579}
[modify] https://crrev.com/0c6213902cc35b2c9c954bafdf61a844a94cbe8c/third_party/WebKit/LayoutTests/TestExpectations