Only return focus if focus was inside the popover before it closed

If a user opens a popover, and then tab-navigates away from the
popover and the invoker, then it is unexpected that focus returns
to the popover invoker when the popover closes. This CL changes
the behavior so that focus is only returned if the current focus
is within the (shadow including) tree of the popover.

Fixed: 1422277
Bug: 1307772
Change-Id: Ibeb2646d2d23751108dc231fe2f23ff7570cd6e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4322607
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Auto-Submit: Mason Freed <masonf@chromium.org>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1116643}