REGRESSION (r245170): gmail.com header flickers when hovering over the animating buttons

[Simon Fraser (smfr)]

Steps To Reproduce:
1. Go to gmail.com and login
2. Hover on the emails 

Results:
Headers disappear and reappear.

[Simon Fraser (smfr)]

<rdar://problem/50865946>

[Simon Fraser (smfr)]

Created attachment 370101 [details]
Reduction

[Simon Fraser (smfr)]

I think this is about a negative z-index child that causes its enclosing stacking context to become composited late. If that layer was sharing, we make it non-sharing, but leave the overlap map in a bad state.

[Simon Fraser (smfr)]

Yeah we double-push a container to the overlap map in that case.

[Simon Fraser (smfr)]

Created attachment 370102 [details]
Patch

[EWS Watchlist]

Comment on attachment 370102 [details]
Patch

Attachment 370102 [details] did not pass mac-ews (mac):
Output: https://webkit-queues.webkit.org/results/12212813

Number of test failures exceeded the failure limit.

[EWS Watchlist]

Created attachment 370103 [details]
Archive of layout-test-results from ews102 for mac-highsierra

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews102  Port: mac-highsierra  Platform: Mac OS X 10.13.6

[EWS Watchlist]

Comment on attachment 370102 [details]
Patch

Attachment 370102 [details] did not pass mac-wk2-ews (mac-wk2):
Output: https://webkit-queues.webkit.org/results/12212837

Number of test failures exceeded the failure limit.

[EWS Watchlist]

Created attachment 370104 [details]
Archive of layout-test-results from ews107 for mac-highsierra-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews107  Port: mac-highsierra-wk2  Platform: Mac OS X 10.13.6

[EWS Watchlist]

Comment on attachment 370102 [details]
Patch

Attachment 370102 [details] did not pass mac-debug-ews (mac):
Output: https://webkit-queues.webkit.org/results/12212853

Number of test failures exceeded the failure limit.

[EWS Watchlist]

Created attachment 370105 [details]
Archive of layout-test-results from ews112 for mac-highsierra

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews112  Port: mac-highsierra  Platform: Mac OS X 10.13.6

[EWS Watchlist]

Comment on attachment 370102 [details]
Patch

Attachment 370102 [details] did not pass win-ews (win):
Output: https://webkit-queues.webkit.org/results/12212889

New failing tests:
fast/block/float/list-marker-is-float-crash.html
imported/blink/compositing/video/video-controls-layer-creation-squashing.html
fast/events/media-element-focus-tab.html

[EWS Watchlist]

Created attachment 370106 [details]
Archive of layout-test-results from ews213 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews213  Port: win-future  Platform: CYGWIN_NT-10.0-17763-3.0.5-338.x86_64-x86_64-64bit

[Simon Fraser (smfr)]

Created attachment 370122 [details]
Patch

[Simon Fraser (smfr)]

https://trac.webkit.org/changeset/245471/webkit