Introduce ServiceWorker.EventDispatchingDelay UMA

content/browser/service_worker/service_worker_fetch_dispatcher.cc

Index: content/browser/service_worker/service_worker_fetch_dispatcher.cc
diff --git a/content/browser/service_worker/service_worker_fetch_dispatcher.cc b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
index c08f2659c7b0f86dc4df5b515fd031a8733587c2..ab799ada92e47256bd977b3da35161f95f74eeae 100644
--- a/content/browser/service_worker/service_worker_fetch_dispatcher.cc
+++ b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
@@ -8,8 +8,10 @@
 #include <utility>
 
 #include "base/bind.h"
+#include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/service_worker/embedded_worker_status.h"
+#include "content/browser/service_worker/service_worker_metrics.h"
 #include "content/browser/service_worker/service_worker_version.h"
 #include "content/common/service_worker/service_worker_messages.h"
 #include "content/common/service_worker/service_worker_utils.h"
@@ -76,12 +78,19 @@ ServiceWorkerMetrics::EventType FetchTypeToWaitUntilEventType(
 class ServiceWorkerFetchDispatcher::ResponseCallback {
  public:
   ResponseCallback(base::WeakPtr<ServiceWorkerFetchDispatcher> fetch_dispatcher,
-                   ServiceWorkerVersion* version)
-      : fetch_dispatcher_(fetch_dispatcher), version_(version) {}
+                   ServiceWorkerVersion* version,
+                   const base::Time& start_time)
+      : fetch_dispatcher_(fetch_dispatcher),
+        version_(version),
+        start_time_(start_time) {}
 
   void Run(int request_id,
            ServiceWorkerFetchEventResult fetch_result,
-           const ServiceWorkerResponse& response) {
+           const ServiceWorkerResponse& response,
+           base::Time event_dispatch_time) {
+    ServiceWorkerMetrics::RecordFetchEventDispatchingDelay(
+        event_dispatch_time - start_time_, version_->site_for_uma());
+
     const bool handled =
         (fetch_result == SERVICE_WORKER_FETCH_EVENT_RESULT_RESPONSE);
     if (!version_->FinishRequest(request_id, handled))
@@ -96,6 +105,7 @@ class ServiceWorkerFetchDispatcher::ResponseCallback {
   base::WeakPtr<ServiceWorkerFetchDispatcher> fetch_dispatcher_;
   // Owns |this|.
   ServiceWorkerVersion* version_;
+  base::Time start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(ResponseCallback);
 };
@@ -197,8 +207,8 @@ void ServiceWorkerFetchDispatcher::DispatchFetchEvent() {
       FetchTypeToWaitUntilEventType(request_->fetch_type),
       base::Bind(&ServiceWorkerUtils::NoOpStatusCallback));
 
-  ResponseCallback* response_callback =
-      new ResponseCallback(weak_factory_.GetWeakPtr(), version_.get());
+  ResponseCallback* response_callback = new ResponseCallback(
+      weak_factory_.GetWeakPtr(), version_.get(), base::Time::Now());
   version_->RegisterRequestCallback<ServiceWorkerHostMsg_FetchEventResponse>(
       response_id,
       base::Bind(&ServiceWorkerFetchDispatcher::ResponseCallback::Run,