[App Management] Implement permission live updates.

This CL makes the ExtensionApps class a content settings observer.
This allows live updates to the app management permissions page for a
PWA when the site settings corresponding to that PWA are changed.

Bug: 906508
Change-Id: I9c1a50765b492903e6540d87d7bdb3cb3bedb7bb
Reviewed-on: https://chromium-review.googlesource.com/c/1420499
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Nigel Tao <nigeltao@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Commit-Queue: Reka Norman <rekanorman@google.com>
Cr-Commit-Position: refs/heads/master@{#626858}
5 files changed