GitLab

This CL:
1. Added a new class AmbientModeState to store states related to this
mode.
2. Wired up AssistantManagerServiceImpl to observe the new state change in
order to update action module as necessary.

Misc:
Fixed linter warnings.

Bug: b/139698911
Test: run unittests added in this change
Change-Id: I4dd078c19cc2ce73a8262fe3cfc0c39308949e82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1906932
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721894}