Log operator code histogram on new metric log

chrome/browser/metrics/metrics_service_observer.h

Index: chrome/browser/metrics/metrics_service_observer.h
diff --git a/chrome/browser/metrics/metrics_service_observer.h b/chrome/browser/metrics/metrics_service_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..045f8e1c30c80e2a973bcb6676d2e3b4b0ea76f8
--- /dev/null
+++ b/chrome/browser/metrics/metrics_service_observer.h
@@ -0,0 +1,25 @@
+// 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_OBSERVER_H_
+#define CHROME_BROWSER_METRICS_METRICS_SERVICE_OBSERVER_H_
+
+#include "base/macros.h"
+
+// MetricsServiceObserver receives notifications from MetricsService.
+// An observer must be added, removed, and notified in the same thread.

[Ilya Sherman, 2014/05/07 23:57:40]

nit: "in the same thread" -> "on the same thread".  The MetricsService class is
not thread safe, and runs on the main thread.

[bolian, 2014/05/08 00:54:52]

Done.

+class MetricsServiceObserver {
+ public:
+  // Called when a new MetricsLog is created.
+  virtual void OnDidCreateMetricsLog() = 0;
+
+ protected:
+  MetricsServiceObserver() {}
+  virtual ~MetricsServiceObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MetricsServiceObserver);
+};
+
+#endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_OBSERVER_H_