REGRESSION (r266972): [ Mojave+ debug wk2 ] compositing/animation/repaint-after-clearing-shared-backing.html is a flaky failure

• Component: Animations
• Status: RESOLVED FIXED

[Karl Rackler]

Description:
compositing/animation/repaint-after-clearing-shared-backing.html

The first failure that I see this on the dashboard was 09/12/20 at r266974, but is not relevant to what would have caused this.
The test was introduced at r266972 and has been flaky failure since then.

The test was expecting a fader margin: 50px;height: 200px;background-color: rgba(255, 255, 255, 0.5); but returned fader with larger width and position higher.

REPRODUCTION STEPS
Command: 
run-webkit-tests --exit-after-n-failures 1 --iterations 50 --debug compositing/animation/repaint-after-clearing-shared-backing.html

Result: 
Regressions: Unexpected image-only failures (1)
  compositing/animation/repaint-after-clearing-shared-backing.html [ ImageOnlyFailure ]

History:
https://results.webkit.org/?suite=layout-tests&test=compositing%2Fanimation%2Frepaint-after-clearing-shared-backing.html&limit=50000&platform=mac&style=debug&flavor=wk2

Image Results:
https://build.webkit.org/results/Apple-Mojave-Debug-WK2-Tests/r268273%20(12483)/compositing/animation/repaint-after-clearing-shared-backing-diffs.html

[Radar WebKit Bug Importer]

<rdar://problem/70157935>

[Karl Rackler]

I have marked this test as image only failure while this issue is investigated.
https://trac.webkit.org/changeset/268297/webkit

[Antoine Quint]

Created attachment 413152 [details]
Patch

[Antoine Quint]

Committed r269367: <https://trac.webkit.org/changeset/269367>