Prerender: Confirm ServiceWorkers are invoked for NoState Prefetch

content/public/browser/service_worker_context.h

Index: content/public/browser/service_worker_context.h
diff --git a/content/public/browser/service_worker_context.h b/content/public/browser/service_worker_context.h
index c095f9d1314c7fe028441bb19479c2f73d4fc99e..6874423f4600e669eed81f1d9b97df4d1828bfd8 100644
--- a/content/public/browser/service_worker_context.h
+++ b/content/public/browser/service_worker_context.h
@@ -125,6 +125,12 @@ class ServiceWorkerContext {
   // This function can be called from any thread.
   virtual void StopAllServiceWorkersForOrigin(const GURL& origin) = 0;
 
+  // As above, but |callback| is executed when a running worker is stopped. If
+  // there is no running worker, |callback| will never be executed.

[horo, 2017/01/05 05:33:58]

Please write comment that the |callback| is executed on the IO thread.

I think the |callback| should be executed when all workers are stopped.
And even if there is no worker we should execute |callback|.

[mattcary, 2017/01/05 14:30:43]

Done.

Note that the RunSoon helper defined in service_worker_context_wrapper.cc
doesn't check for the callback being null; is that worth adding or should I keep
the code as-is?

[horo, 2017/01/06 02:27:41]

The |callback| should be called only once when the "all" running workers are
stopped. Not "each".
Could you please change the code using BarrierClosure?
I don't think we need the null check.

[mattcary, 2017/01/06 15:21:22]

Ah, I misunderstood. That's a good idea, done.
done

+  virtual void StopAllServiceWorkersForOriginWithCallback(
+      const GURL& origin,
+      const base::Closure& callback) = 0;
+
   // Stops all running service workers and unregisters all service worker
   // registrations. This method is used in LayoutTests to make sure that the
   // existing service worker will not affect the succeeding tests.