Move more metrics classes to metrics namespace.

chrome/browser/chrome_browser_metrics_service_observer.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_CHROME_BROWSER_METRICS_SERVICE_OBSERVER_H_
 #define CHROME_BROWSER_CHROME_BROWSER_METRICS_SERVICE_OBSERVER_H_
 
 #include "components/metrics/metrics_service_observer.h"
 
 // ChromeBrowserMetricsServiceObserver receives notifications when the metrics
 // service creates a new metrics log.
-class ChromeBrowserMetricsServiceObserver : public MetricsServiceObserver {
+class ChromeBrowserMetricsServiceObserver
+    : public metrics::MetricsServiceObserver {
  public:
   ChromeBrowserMetricsServiceObserver();
   virtual ~ChromeBrowserMetricsServiceObserver();
 
   // MetricsServiceObserver:
   virtual void OnDidCreateMetricsLog() OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserMetricsServiceObserver);
 };
 
 #endif  // CHROME_BROWSER_CHROME_BROWSER_METRICS_SERVICE_OBSERVER_H_