GitLab

- Add ShelfLayoutManager::OnWorkAreaInsetsChanged that notifies
  Shelf when it updates the Shelf insets in WorkAreaInsets;
- Add ShelfObserver::OnShelfWorkAreaInsetsChanged that gets called
  when Shelf gets a OnWorkAreaInsetsChanged call;
- AshPopupAlignmentDelegate observes OnShelfWorkAreaInsetsChanged
  and update its work area instead Shelf visibility or autohide
  state change;

Bug: 1002003
Change-Id: I1239713a1d1dd7c27d84cfe4f81621f4ab638ecf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1795907
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695332}