[reading-flow] display: contents as scope owner
We redefine a reading flow scope owner as either:
- it is a reading flow container
- it is a display: contents whose closest layout parent is a reading
flow container
We add the helper function ReadingFlowContainerOrDisplayContents(),
IsReadingFlowScopeOwner() and change reading_flow_container_ to be
Member.
The explainer changes are detailed here:
explainers-by-googlers/css-reading-flow#4
Change-Id: I974ce789578ebd81240608856f758f2bf716222d
Bug: 40932006
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5784682
Commit-Queue: Di Zhang dizhangg@chromium.org
Reviewed-by: Mason Freed masonf@chromium.org
Cr-Commit-Position: refs/heads/main@{#1342510}