[Chromecast] Add an alarm manager for firing events on wall clock time.
PostDelayedTask is subject to time changes, clock drifts, and other factors.
Long duration tasks are even more sensitive.
Polling the wall clock every 5 seconds will allow execution close to the
requested time. If the process is suspended, the task will fire within
5 seconds of being woken up.
BUG= internal b/33114736
Review-Url: https://codereview.chromium.org/2695223008
Cr-Commit-Position: refs/heads/master@{#452335}
4 files changed
