GitLab

This corrects two issues with suspend:
* Ambient mode does not restart when waking up from suspend
* Flash of old Ambient mode photo displays when opening lid from suspend

Block Ambient mode from restarting after |SuspendImminent| until
|SuspendDone| is received. Upon |SuspendDone|, also restart Ambient mode
lock screen timeout if appropriate.

Start Ambient mode, close lid while active. Reopen lid, wait 7 seconds,
Ambient mode starts again over lock screen.

BUG=b:177325727
BUG=b:177692036
TEST=ash_unittest --gtest_filter="AmbientControllerTest.*Suspend"

Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome
Change-Id: I8d52af80ab7dd49538998d0e8831ee3c10d2919a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625727
Commit-Queue: Jeffrey Young <cowmoo@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845384}