ThreadWatcher - generate crash dump if ThreadWatcher doesn't disarm

StartupTimeBomb in 10 minutes.

Give more time for startup tasks to finish.

R=sky@chromium.org
BUG=396356

Review URL: https://codereview.chromium.org/581163003

Cr-Commit-Position: refs/heads/master@{#295593}

chrome/browser/chrome_browser_main.cc

@@ -1422,7 +1422,7 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
   metrics::MetricsService::SetExecutionPhase(
       metrics::MetricsService::STARTUP_TIMEBOMB_ARM,
       g_browser_process->local_state());
-  startup_watcher_->Arm(base::TimeDelta::FromSeconds(300));
+  startup_watcher_->Arm(base::TimeDelta::FromSeconds(600));
 
   // On mobile, need for clean shutdown arises only when the application comes
   // to foreground (i.e. MetricsService::OnAppEnterForeground is called).