Use base::HeapArray in content/browser/accessibility/

Fixed: 326458536
Fixed: 326458496
Change-Id: I9b7e9fe77d0e81b0c55695223c7deaf9a6edf130
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402117


Reviewed-by: Benjamin Beaudry <benjamin.beaudry@microsoft.com>
Auto-Submit: Avi Drissman <avi@chromium.org>
Commit-Queue: Benjamin Beaudry <benjamin.beaudry@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1279305}