Split out MetricsServiceAccessor out of ChromeMetricsServiceAccessor.

chrome/browser/metrics/metrics_service_accessor.h

Index: chrome/browser/metrics/metrics_service_accessor.h
diff --git a/chrome/browser/metrics/metrics_service_accessor.h b/chrome/browser/metrics/metrics_service_accessor.h
new file mode 100644
index 0000000000000000000000000000000000000000..26ce88e7dee4818947d263edf76809fc339dd0f5
--- /dev/null
+++ b/chrome/browser/metrics/metrics_service_accessor.h
@@ -0,0 +1,30 @@
+// 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 "base/macros.h"
+
+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. Decendants should
+  // disallow instantiation.
+  MetricsServiceAccessor() {}
+
+  // Registers/unregisters |observer| to receive MetricsLog notifications
+  // from metrics service.
+  static void AddMetricsServiceObserver(MetricsServiceObserver* observer);
+  static void RemoveMetricsServiceObserver(MetricsServiceObserver* observer);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MetricsServiceAccessor);
+};
+
+#endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_