Merge of "Add metrics regarding concurrent audible tabs in Chromium."

These metrics are keeping track of:
- whether there is another audible tab when a tab becomes audible;
- the maximum number of concurrent audible tab in a session;
- how long there are 2 or more audible tabs at the same time.

It is also recording when a tab gain or loses audible status.

BUG=578049

Review URL: https://codereview.chromium.org/1591453005

Cr-Commit-Position: refs/heads/master@{#370435}
(cherry picked from commit 44e4ef4)

Review URL: https://codereview.chromium.org/1618523003 .

Cr-Commit-Position: refs/branch-heads/2623@{#44}
Cr-Branched-From: 92d7753-refs/heads/master@{#369907}

content/browser/media/audible_metrics.cc

@@ -0,0 +1,79 @@
+// 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.
+
+#include "content/browser/media/audible_metrics.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/metrics/user_metrics.h"
+#include "base/time/default_tick_clock.h"
+
+namespace content {
+
+AudibleMetrics::AudibleMetrics()
+    : max_concurrent_audible_web_contents_in_session_(0),
+      clock_(new base::DefaultTickClock()) {
+}
+
+AudibleMetrics::~AudibleMetrics() {
+}
+
+void AudibleMetrics::UpdateAudibleWebContentsState(
+    const WebContents* web_contents, bool audible) {
+  bool found =
+      audible_web_contents_.find(web_contents) != audible_web_contents_.end();
+  if (found == audible)
+    return;
+
+  if (audible)
+    AddAudibleWebContents(web_contents);
+  else
+    RemoveAudibleWebContents(web_contents);
+}
+
+void AudibleMetrics::SetClockForTest(scoped_ptr<base::TickClock> test_clock) {
+  clock_ = std::move(test_clock);
+}
+
+void AudibleMetrics::AddAudibleWebContents(const WebContents* web_contents) {
+  base::RecordAction(base::UserMetricsAction("Media.Audible.AddTab"));
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Media.Audible.ConcurrentTabsWhenStarting", audible_web_contents_.size(),
+      1, 10, 11);
+
+  audible_web_contents_.insert(web_contents);
+  if (audible_web_contents_.size() > 1 &&
+      concurrent_web_contents_start_time_.is_null()) {
+    concurrent_web_contents_start_time_ = clock_->NowTicks();
+  }
+
+  if (audible_web_contents_.size() >
+      max_concurrent_audible_web_contents_in_session_) {
+    max_concurrent_audible_web_contents_in_session_ =
+        audible_web_contents_.size();
+
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "Media.Audible.MaxConcurrentTabsInSession",
+        max_concurrent_audible_web_contents_in_session_,
+        1, 10, 11);
+  }
+}
+
+void AudibleMetrics::RemoveAudibleWebContents(const WebContents* web_contents) {
+  base::RecordAction(base::UserMetricsAction("Media.Audible.RemoveTab"));
+
+  audible_web_contents_.erase(web_contents);
+
+  if (audible_web_contents_.size() <= 1 &&
+      !concurrent_web_contents_start_time_.is_null()) {
+    base::TimeDelta concurrent_total_time =
+        clock_->NowTicks() - concurrent_web_contents_start_time_;
+    concurrent_web_contents_start_time_ = base::TimeTicks();
+
+    UMA_HISTOGRAM_LONG_TIMES("Media.Audible.ConcurrentTabsTime",
+                             concurrent_total_time);
+  }
+}
+
+}  // namespace content

content/browser/media/audible_metrics.h

@@ -0,0 +1,49 @@
+// 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_