Fix clicks on following articles to return to following feed.

When the user was clicking on a following feed article, and returned,
it was coming back to the for you feed, not the following feed.

This change fixes that by rembering which feed we are restoring,
and making sure to set that one back after some methods that
were overwriting it as a side effect.

This change also updates the referrer to be the Following tab
instead of the For you tab.

Bug: b/185822991
Change-Id: I769ea69017c7d8f19eacba802b36b4452d198b30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2869973
Reviewed-by: Peter Williamson <petewil@chromium.org>
Reviewed-by: Cathy Li <chili@chromium.org>
Commit-Queue: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879380}