[App Management] Integrate search view with dom-switch

This CL integrates search view with dom-switch by letting selectedRouteId_ directly watch the
existence of search term rather than delegating to reducer.currentPageState to handle search.

This way, after users clear search, they will go back to the page they were on rather than main
page.

Bug: 906508
Change-Id: I75aabf2ccfdadc48093062b48adf85932c2b9606
Reviewed-on: https://chromium-review.googlesource.com/c/1459868
Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Cecilia Ni <ceciliani@google.com>
Cr-Commit-Position: refs/heads/master@{#630699}
7 files changed