Revert^2 "Reland "[A11y] Do not allow asymmetrical parent-child relations in tree""

[chromium-wpt-export-bot]

This reverts commit 7d71be73ff6ae1e26559634149c729b41de71836.

Reason for revert: Reverting this cl makes the failure stable. reland this.

Original change's description:

Revert "Reland "[A11y] Do not allow asymmetrical parent-child relations in tree""

This reverts commit 8fda0f8317a6f861c97c413d1deecb8c4f998481.

Reason for revert: Test failure on Linux MSan Tests: https://ci.chromium.org/ui/b/8764197885202278033

Original change's description:

Reland "[A11y] Do not allow asymmetrical parent-child relations in tree"

This is a reland of commit 0953e5a0ef7748af2c932568ec9d9bbdbc480f11

Two new tests have been added since the original CL:

1. content/test/data/regression/aria-owns-from-textarea.html, which
   induces the same crash as google.com, which caused the revert via bug 1501535. The fix for this one is to not assume the owned child had
   previously been unignored.
2. web_tests/accessibility/aria-owns-dynamic-changes-2.html, to show that the consequences of the error Chris found in the original landing as discussed in this review thread: https://chromium-review.googlesource.com/c/chromium/src/+/4873421/72..77/third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.cc#b1418
   The fix for this one was already in the original landing.

Original change's description:

[A11y] Do not allow asymmetrical parent-child relations in tree

Design doc:
https://docs.google.com/document/d/1PnjhlWqTtivmsUVTF0kqMAUIsO9a_eTp32pRY4KJh_U/edit#heading=h.wlgzk7gh4m76

Fix failures brought to light by the Eager AX Tree Updates project and related checks, so that serialization operates on a truly frozen, complete AX Tree, and does not lead to changes to the underlying data at unsafe times. After landing this CL and any follow-ups, the goal is to have a vastly more stable, predictable Blink accessibility engine.

The current implementation can lead to processing the tree when there
are "holes" in the data structure, such as missing parents or children,
which can lead to crashes, checks and unpredictability.

1. Avoid holes in the first place: do not call AXObject::ClearChildren() immediately when calling AXObject::SetNeedsToUpdateChildren(), so that missing parent and missing child holes are not created for unchanged siblings. These holes tended to sit around and cause problems when downstream operations did not expect them. Only call ClearChildren() right before rebuilding the children, in UpdateChildrenIfNecessary().
2. More complete repairs: Instead of only repairing missing parents, when a parentless ensure a complete subtree structure around the child, starting with the included parent. The new method to accomplish this is called AXObjectCacheImpl::RepairIncludedParentsChildren(). It makes sure that every parent up to the included parent has a complete set of children.
3. More timely repairs: instead of waiting for a hole to be discovered while tree walking, eagerly ensure that objects up to their included parent have repairs, whenever an object is being retrieved for deferred event processing, or when an object is being created in the middle of a tree. If the necessary parents do not exist, and thus the AXObject itself is not viable, make sure any stale AXObjects in that subtree are eagerly removed, because they are also not viable.
4. More complete tree structure checks in AXObjectCacheImpl::CheckTreeIsUpdated(), which ensure symmetrical included parent-child relationships are complete. This helps guarantee that no lazy computations try to alter the tree while it’s being serialized (in a frozen state). The new checks do not pass without the other code changes, which are in service of the new checks.

Future work: attempt to avoid any tree repairs and guarantee completeness in more places, providing even more predictability, for example, by handling CSS display changes similarly to role changes.

Fixed: 1422755,1483877,1482591,1481940,1480442,1488246,1486249,1484029,1353205,1480627,1494849,1493953,1484394,1489027,1491163,1501723
Change-Id: Ied4258680ffe4099caaf4c5e614c59c70c61a013
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4873421
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1223164}

Change-Id: I96fcc71601842ea7b38de70ee24f77df1f011f24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5019353
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1225907}

Change-Id: I77f6149192a7afa697098e125900705ab43ed0f0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1503056
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5040555
Reviewed-by: Yifan Luo <lyf@chromium.org>
Owners-Override: Yifan Luo <lyf@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1225985}

Bug: 1503056
Change-Id: Id9b4319eefa91a2988adda94fb69bc1881c63600
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5038755
Auto-Submit: Yifan Luo <lyf@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Yifan Luo <lyf@chromium.org>
Reviewed-by: Yifan Luo <lyf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1226026}

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.