[ServiceWorker] Convert ping-pong IPC into mojo interface ServiceWorkerEventDispatcher

content/common/service_worker/service_worker_event_dispatcher.mojom

Index: content/common/service_worker/service_worker_event_dispatcher.mojom
diff --git a/content/common/service_worker/service_worker_event_dispatcher.mojom b/content/common/service_worker/service_worker_event_dispatcher.mojom
index e47c085b9d9a8c9588cff6af96e73398ec7e75e2..6162b1d8ca0d6a474b82cd3aaf1573815e1f0300 100644
--- a/content/common/service_worker/service_worker_event_dispatcher.mojom
+++ b/content/common/service_worker/service_worker_event_dispatcher.mojom
@@ -73,4 +73,10 @@ interface ServiceWorkerEventDispatcher {
   DispatchExtendableMessageEvent(ExtendableMessageEvent event)
       => (blink.mojom.ServiceWorkerEventStatus status,
           mojo.common.mojom.Time dispatch_event_time);
+
+  // Pings the service worker to check if it is responsive. If the callback is
+  // not called within a certain period of time, the browser will terminate the
+  // worker. Unlike the other functions in this interface, Ping() does not
+  // dispatch an event.
+  Ping() => ();

[falken, 2017/03/22 05:46:30]

Just to be sure, we are guaranteed Ping() is called on the service worker
thread, right?

[leonhsl(Using Gerrit), 2017/03/22 06:45:59]

From my current knowledge, in browser side SWVersion calls this mojo function
Ping() on IO thread, and in renderer side SWContextClient executes its impl of
Ping() on its own service worker thread. Hopefully I'm understanding correctly
:)

[shimazu, 2017/03/22 06:46:26]

Yeah, ServiceWorkerEventDispather is bound after the worker thread has started.

 };