[App Management] Add onAppChanged and onAppRemoved listeners.

This CL adds actions and reducers to handle the onAppChanged and
onAppRemoved events, as well as tests for these reducers.

Bug: 906508
Change-Id: I7b809e1030f33ea772a8d74343b45189f199f1fe
Reviewed-on: https://chromium-review.googlesource.com/c/1375290
Commit-Queue: Reka Norman <rekanorman@google.com>
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616549}
4 files changed