Add metrics regarding concurrent audible tabs in Chromium.

content/browser/media/audible_metrics.h

+// 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/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:

[whywhat, 2016/01/15 19:01:19]

nit: s/%/It reports three different metrics/ ?

+// - 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(WebContents* web_contents, bool audible);

[DaleCurtis, 2016/01/15 19:02:03]

const all usage of WebContents* in this class.

[mlamouri (slow - plz ping), 2016/01/19 19:26:36]

Done.

+
+  void SetClockForTest(scoped_ptr<base::Clock> testing_clock);
+
+ private:
+  void AddAudibleWebContents(WebContents* web_contents);
+  void RemoveAudibleWebContents(WebContents* web_contents);
+
+  base::Time concurrent_web_contents_start_time_;

[DaleCurtis, 2016/01/15 19:02:03]

TimeTicks

[DaleCurtis, 2016/01/19 18:36:53]

Don't see any resolution or discussion of this comment or the TickClock one
below it? 

[mlamouri (slow - plz ping), 2016/01/19 19:26:36]

I think I missed the first file entirely. Sorry about that. I happened to have
applied all comments but that one but it's just because I saw them while
re-reading the patch :)

Should be fixed now.

+  size_t max_concurrent_audible_web_contents_in_session_;
+  scoped_ptr<base::Clock> clock_;

[DaleCurtis, 2016/01/15 19:02:03]

TickClock to avoid time going backwards issues

[mlamouri (slow - plz ping), 2016/01/19 19:26:36]

Done.

+
+  std::set<WebContents*> audible_web_contents_;
+};

[DaleCurtis, 2016/01/15 19:02:03]

DISALLOW_COPY_AND_ASSIGN

[mlamouri (slow - plz ping), 2016/01/19 19:26:36]

Done.

+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_AUDIBLE_METRICS_H_