[Autofill Assistant] Verify password origin before entering

This adds a safety check that the element's frame is in the same,
or sub-, domain of the password's origin.
If not, an error is returned.

Bug: b/154174137
Bug: b/154067717
Change-Id: I7adeaf00fb34d867ab70cbc9ac06faa31ceb7eab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2767221


Commit-Queue: Sandro Maggi <sandromaggi@google.com>
Reviewed-by: Clemens Arbesser <arbesser@google.com>
Cr-Commit-Position: refs/heads/master@{#865075}