Remove MetricsServiceObserver in favor of MetricsProvider.

chrome/browser/metrics/metrics_service_accessor.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 CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_
 
 #include <stdint.h>
-#include <string>
 
 #include "base/macros.h"
 
 namespace metrics {
 class MetricsService;
-class MetricsServiceObserver;
 }
 
 // This class limits and documents access to metrics service helper methods.
 // These methods are protected so each user has to inherit own program-specific
 // specialization and enable access there by declaring friends.
 class MetricsServiceAccessor {
  protected:
   // Constructor declared as protected to enable inheritance. Descendants should
   // disallow instantiation.
   MetricsServiceAccessor() {}
 
-  // Registers/unregisters |observer| to receive MetricsLog notifications
-  // from metrics service.
-  static void AddMetricsServiceObserver(
-      metrics::MetricsServiceObserver* observer);
-  static void RemoveMetricsServiceObserver(
-      metrics::MetricsServiceObserver* observer);
-
   // Registers the specified synthetic field trial (identified by a hash of the
   // trial name and group name) with |metrics_service|, if the service is not
   // NULL, returning true on success.
   // See the comment on MetricsService::RegisterSyntheticFieldTrial for details.
   static bool RegisterSyntheticFieldTrial(
       metrics::MetricsService* metrics_service,
       uint32_t trial_name_hash,
       uint32_t group_name_hash);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsServiceAccessor);
 };
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_