service worker: Skip recording timing when wait for debugger is on.

We were skipping recording for the legacy EmbeddedWorkerInstance
metrics but not the ServiceWorker.StartTiming.* metrics.

It doesn't look like there's been a big effect regardless.

Bug: 855952
Change-Id: I4f2804e45e75b6fa4f7bded732e7e472e2033bdf
Reviewed-on: https://chromium-review.googlesource.com/1122060Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571862}

content/browser/service_worker/embedded_worker_instance.cc

@@ -683,6 +683,7 @@ void EmbeddedWorkerInstance::OnRegisteredToDevToolsManager(
     // We don't measure the start time when wait_for_debugger flag is set. So
     // we set the NULL time here.
     step_time_ = base::TimeTicks();
+    inflight_start_task_->set_skip_recording_startup_time();
   }
   for (auto& observer : listener_list_)
     observer.OnRegisteredToDevToolsManager();