S13nServiceWorker: Fix `fetchStart` performance timing for subresources

ServiceWorkerSubresourceLoader records loading milestones. These
milestones are used to create web-exposed PerformanceResourceTiming.

Before this CL, ServiceWorkerSubresourceLoader recorded
|service_worker_ready_time| before calling GetControllerServiceWorker().
This doesn't seem a good timing to record it because:
- |service_worker_ready_time| is used to create `fetchStart` of
  PerformanceResourceTiming.
- `fetchStart` should be recorded after the controller service worker is
  ready to handle fetch event.
- But the worker may not be running until we call GetControllerServiceWorker().

This CL moves the timing to record |service_worker_raedy_time| and some others
after calling GetControllerServiceWorker(), as calling it makes sure that
the controller is running and ready to handle a fetch event.

The wpt ervice-workers/service-worker/resource-timing.https.html should
cover this change.

Bug: 782958
Change-Id: Ic6f6abd34ffdc84e002357a905e7a7726e6b5870
Reviewed-on: https://chromium-review.googlesource.com/1212244
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589818}

content/renderer/service_worker/service_worker_subresource_loader.cc

@@ -200,11 +200,6 @@ void ServiceWorkerSubresourceLoader::StartRequest(
   fetch_request_restarted_ = false;
 
   response_head_.service_worker_start_time = base::TimeTicks::Now();
-  // TODO(horo): Reset |service_worker_ready_time| when the the connection to
-  // the service worker is revived.
-  response_head_.service_worker_ready_time = base::TimeTicks::Now();
-  response_head_.load_timing.send_start = base::TimeTicks::Now();
-  response_head_.load_timing.send_end = base::TimeTicks::Now();
   DispatchFetchEvent();
 }
 
@@ -214,6 +209,14 @@ void ServiceWorkerSubresourceLoader::DispatchFetchEvent() {
   mojom::ControllerServiceWorker* controller =
       controller_connector_->GetControllerServiceWorker(
           mojom::ControllerServiceWorkerPurpose::FETCH_SUB_RESOURCE);
+
+  // GetControllerServiceWorker() makes sure that the connection to the
+  // service worker is established, which means that the service worker
+  // has started if it wasn't running.
+  response_head_.service_worker_ready_time = base::TimeTicks::Now();
+  response_head_.load_timing.send_start = base::TimeTicks::Now();
+  response_head_.load_timing.send_end = base::TimeTicks::Now();
+
   TRACE_EVENT1("ServiceWorker",
                "ServiceWorkerSubresourceLoader::DispatchFetchEvent",
                "controller", (controller ? "exists" : "does not exist"));