ServiceWorker: Bypass SW when the script doesn't have fetch handler

content/browser/service_worker/service_worker_controllee_request_handler.cc

Index: content/browser/service_worker/service_worker_controllee_request_handler.cc
diff --git a/content/browser/service_worker/service_worker_controllee_request_handler.cc b/content/browser/service_worker/service_worker_controllee_request_handler.cc
index 7b9b35c2f65f13ebd0b38aab55b6107763f09df3..181dc951909e50900f54fc224d36a7786fc0904e 100644
--- a/content/browser/service_worker/service_worker_controllee_request_handler.cc
+++ b/content/browser/service_worker/service_worker_controllee_request_handler.cc
@@ -252,7 +252,11 @@ ServiceWorkerControlleeRequestHandler::DidLookupRegistrationForMainResource(
 
   ServiceWorkerMetrics::CountControlledPageLoad(stripped_url_);
 
-  job_->ForwardToServiceWorker();
+  if (!active_version->has_fetch_handler())
+    job_->FallbackToNetwork();
+  else
+    job_->ForwardToServiceWorker();
+
   TRACE_EVENT_ASYNC_END2(
       "ServiceWorker",
       "ServiceWorkerControlleeRequestHandler::PrepareForMainResource",
@@ -282,7 +286,11 @@ void ServiceWorkerControlleeRequestHandler::OnVersionStatusChanged(
 
   provider_host_->AssociateRegistration(registration,
                                         false /* notify_controllerchange */);
-  job_->ForwardToServiceWorker();
+
+  if (!version->has_fetch_handler())
+    job_->FallbackToNetwork();
+  else
+    job_->ForwardToServiceWorker();
 }
 
 void ServiceWorkerControlleeRequestHandler::DidUpdateRegistration(
@@ -352,7 +360,10 @@ void ServiceWorkerControlleeRequestHandler::PrepareForSubResource() {
   DCHECK(job_.get());
   DCHECK(context_);
   DCHECK(provider_host_->active_version());
-  job_->ForwardToServiceWorker();
+  if (!provider_host_->active_version()->has_fetch_handler())
+    job_->FallbackToNetwork();
+  else
+    job_->ForwardToServiceWorker();

[falken, 2016/05/27 09:53:34]

Can you factor out these three blocks into a helper function?

(Another option may be to skip the SW machinery completely by having 
ServiceWorkerProviderHost::CreateRequestHandler check if the controlling version
has a fetch handler. That may be faster than creating this job that will just
bail out. However, if we do that, the update scheduler in
~ServiceWorkerControlleeRequestHandler won't run for subresources. So possibly
the page load time is hurt by the update job. That could be worked around by
having CreateRequestHandler call DeferScheduleUpdate though, but that's getting
a bit ugly.)

[shimazu, 2016/05/30 05:41:59]

I roughly checked the performance improvements by implementing this and browsing
some pages w/o fetch handler with DevTools, but there seems to be no visible
improvements of performance, so I think it's better to take cleanness of codes.

Done.

 }
 
 void ServiceWorkerControlleeRequestHandler::OnPrepareToRestart() {