[mparch] Use PrimaryPageChanged in FaviconTabHelper.

This CL replaces DidFinishNavigation with PrimaryPageChanged in
FaviconTabHelper. Listening to PrimaryPageChanged is preferred to
listening to DidFinishNavigation and checking IsInPrimaryMainFrame,
!IsSameDocument, and HasCommitted.

Bug: 1269645
Change-Id: If7017b0e3b7269edf413a33fe3bede6c3d8b819c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3622174
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Commit-Queue: Hyowon Kim <hyowon@igalia.com>
Reviewed-by: Bo Liu <boliu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#999169}