Revert "Reland "Refactor to handle ignored nodes that pass into the browser AX tree""

This reverts commit febfd29fbb5527e1f6d38ef3d7ac5d5737021020.

Reason for revert: Cause of https://crbug.com/965139

Original change's description:
> Reland "Refactor to handle ignored nodes that pass into the browser AX tree"
> 
> 
> This re-lands this CL:
> https://chromium-review.googlesource.com/c/chromium/src/+/1535171
> 
> Which was reverted here:
> https://chromium-review.googlesource.com/c/chromium/src/+/1610026
> 
> Original Change's description:
> > Refactor to handle ignored nodes that pass into the browser AX tree
> >
> > * Introduces the concept of "in the tree" vs "ignored" in Blink without
> >   changing the actual behavior. No ignored nodes are sent to the browser
> >   accessibility tree.
> > * Adds new function IsIgnoredPassThrough, for use when an object is
> >   ignored, but should be passed through to the browser-side anyways.
> >   This will be used to allow different types of ignored nodes to pass
> >   through, instead of all at once.
> > * Refactors browser-side code to walk only the unignored tree.
> >
> > Bug: 651614
> >
> > Change-Id: Idbd85949a8505f8a03a08e3e002bb893619d6757
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535171
> > Commit-Queue: Jacques Newman <janewman@microsoft.com>
> > Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> > Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
> > Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
> > Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
> > Cr-Commit-Position: refs/heads/master@{#659089}
> 
> Change additional to original change:
> The original change caused a crash because GetUnignoredChildCount was
> called on a parent with dangling pointers in its children vector.
> This was previously acceptable as child_count only relied on the
> length of the vector, not its contents.
> This issue has been mitigated by caching the unignored child count,
> similar to how the unignored index in parent is cached.
> 
> Bug: 651614
> 
> Change-Id: I90b09237862d17848113fb084b9b08b60e12999f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609590
> Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
> Commit-Queue: Jacques Newman <janewman@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#660987}

TBR=kinuko@chromium.org,aboxhall@chromium.org,kbabbitt@microsoft.com,janewman@microsoft.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 651614
Change-Id: I187996e894835447905c3d9a10faceedf60b9a54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1620907
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661463}
26 files changed