Shutdown Timebomb - In canary, get a callstack if it takes longer than
10 minutes. In Dev, get callstack if it takes longer than 20 minutes.
In Beta (50 minutes) and Stable (100 minutes) it is same as before.

BUG=519321
R=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/1409333005

Cr-Commit-Position: refs/heads/master@{#355586}
void ThreadWatcherObserver::OnUserActivityDetected() {
  base::TimeTicks now = base::TimeTicks::Now();
  if ((now - last_wakeup_time_) < wakeup_interval_)
    return;
  last_wakeup_time_ = now;
  WatchDogThread::PostTask(
      FROM_HERE,
      base::Bind(&ThreadWatcherList::WakeUpAll));
}

void ThreadWatcherObserver::OnUserActivityDetected() {
  base::TimeTicks now = base::TimeTicks::Now();
  if ((now - last_wakeup_time_) < wakeup_interval_)
    return;
  last_wakeup_time_ = now;
  WatchDogThread::PostTask(
      FROM_HERE,
      base::Bind(&ThreadWatcherList::WakeUpAll));
}
