Remove MetricsServiceObserver in favor of MetricsProvider.

components/metrics/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 COMPONENTS_METRICS_METRICS_SERVICE_OBSERVER_H_
-#define COMPONENTS_METRICS_METRICS_SERVICE_OBSERVER_H_
-
-#include "base/macros.h"
-
-namespace metrics {
-
-// MetricsServiceObserver receives notifications from MetricsService.
-// An observer must be added, removed, and notified on the same thread.
-class MetricsServiceObserver {
- public:
-  // Called when a new MetricsLog is created.
-  virtual void OnDidCreateMetricsLog() = 0;
-
- protected:
-  MetricsServiceObserver();
-  virtual ~MetricsServiceObserver();
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(MetricsServiceObserver);
-};
-
-}  // namespace metrics
-
-#endif  // COMPONENTS_METRICS_METRICS_SERVICE_OBSERVER_H_