Add async tracing to SWVersion::AddRequest.

content/browser/service_worker/service_worker_metrics.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_
 #define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 73 matching lines @@
     SERVICE_PORT_CONNECT,
     MESSAGE,
     // Add new events to record here.
 
     NUM_TYPES
   };
 
   // Used for UMA. Append only.
   enum class Site { OTHER, NEW_TAB_PAGE, NUM_TYPES };
 
+  // Converts an event type to a string. Used for tracing.
+  static const char* EventTypeToString(EventType event_type);
+
   // Excludes NTP scope from UMA for now as it tends to dominate the stats and
   // makes the results largely skewed. Some metrics don't follow this policy
   // and hence don't call this function.
   static bool ShouldExcludeSiteFromHistogram(Site site);
   static bool ShouldExcludeURLFromHistogram(const GURL& url);
 
   // Used for ServiceWorkerDiskCache.
   static void CountInitDiskCacheResult(bool result);
   static void CountReadResponseResult(ReadResponseResult result);
   static void CountWriteResponseResult(WriteResponseResult result);
@@ skipping 70 matching lines @@
   // previous event ended).
   static void RecordTimeBetweenEvents(const base::TimeDelta& time);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ServiceWorkerMetrics);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_