[toolbarpinning] Return correct anchor view for page actions on minimal toolbar browsers

There exist browsers with minimal toolbars in which the pinned actions
container does not exist. If it does not exist, we return the default
anchor (location bar).

Bug: 358542671
Change-Id: Ic0eae816999f82005e0ff33e14dba26ce7d83328
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5787019
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Caroline Rising <corising@chromium.org>
Auto-Submit: Joseph Park <josephjoopark@chromium.org>
Reviewed-by: Caroline Rising <corising@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1341661}