Decouple Metrics Initialization from IO Thread Initialization

components/metrics/metrics_service.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.
 
 // This file defines a service that collects information about the user
 // experience in order to help improve future versions of the app.
 
 #ifndef COMPONENTS_METRICS_METRICS_SERVICE_H_
 #define COMPONENTS_METRICS_METRICS_SERVICE_H_
 
@@ skipping 188 matching lines @@
   // should not be called more than once.
   void CheckForClonedInstall(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // Clears the stability metrics that are saved in local state.
   void ClearSavedStabilityMetrics();
 
   // Pushes a log that has been generated by an external component.
   void PushExternalLog(const std::string& log);
 
-  // Returns a callback to data use pref updating function which can be called
-  // from any thread, but this function should be called on UI thread.
-  UpdateUsagePrefCallbackType GetDataUseForwardingCallback();
+  // Updates data usage tracking prefs with the specified values.
+  void UpdateMetricsUsagePrefs(const std::string& service_name,
+                               int message_size,
+                               bool is_cellular);
 
   // Merge any data from metrics providers into the global StatisticsRecorder.
   void MergeHistogramDeltas();
 
  protected:
   // Exposed for testing.
   MetricsLogManager* log_manager() { return &log_manager_; }
 
  private:
   friend class MetricsServiceAccessor;
@@ skipping 273 matching lines @@
   // Weak pointers factory used for saving state. All weak pointers managed by
   // this factory are invalidated in ScheduleNextStateSave.
   base::WeakPtrFactory<MetricsService> state_saver_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsService);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_METRICS_SERVICE_H_