Add metrics regarding concurrent audible tabs in Chromium.

content/browser/media/audible_metrics.h

Index: content/browser/media/audible_metrics.h
diff --git a/content/browser/media/audible_metrics.h b/content/browser/media/audible_metrics.h
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+++ b/content/browser/media/audible_metrics.h
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+// Copyright 2016 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 CONTENT_BROWSER_MEDIA_AUDIBLE_METRICS_H_
+#define CONTENT_BROWSER_MEDIA_AUDIBLE_METRICS_H_
+
+#include <set>
+
+#include "base/memory/scoped_ptr.h"
+#include "base/time/tick_clock.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+class WebContents;
+
+// This class handles metrics regarding audible WebContents.
+// It does register three different information:
+// - how many WebContents are audible when a WebContents become audible.
+// - how long multiple WebContents are audible at the same time.
+// - for a browsing session, how often and how many WebContents get audible at
+//   the same time.
+class CONTENT_EXPORT AudibleMetrics {
+ public:
+  AudibleMetrics();
+  ~AudibleMetrics();
+
+  void UpdateAudibleWebContentsState(const WebContents* web_contents,
+                                     bool audible);
+
+  void SetClockForTest(scoped_ptr<base::TickClock> test_clock);
+
+ private:
+  void AddAudibleWebContents(const WebContents* web_contents);
+  void RemoveAudibleWebContents(const WebContents* web_contents);
+
+  base::TimeTicks concurrent_web_contents_start_time_;
+  size_t max_concurrent_audible_web_contents_in_session_;
+  scoped_ptr<base::TickClock> clock_;
+
+  std::set<const WebContents*> audible_web_contents_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudibleMetrics);
+};
+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_AUDIBLE_METRICS_H_