Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/android/media_session_uma_helper.h

-// Copyright 2015 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_ANDROID_MEDIA_SESSION_UMA_HELPER_H_
-#define CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_UMA_HELPER_H_
-
-#include "base/memory/scoped_ptr.h"
-#include "base/time/clock.h"
-#include "content/common/content_export.h"
-
-namespace base {
-class Clock;
-}  // base namespace
-
-namespace content {
-
-class CONTENT_EXPORT MediaSessionUmaHelper {
- public:
-  // This is used for UMA histogram (Media.Session.Suspended). New values should
-  // be appended only and must be added before |Count|.
-  enum class MediaSessionSuspendedSource {
-    SystemTransient = 0,
-    SystemPermanent = 1,
-    UI = 2,
-    CONTENT = 3,
-    SystemTransientDuck = 4,
-    Count // Leave at the end.
-  };
-
-  MediaSessionUmaHelper();
-  ~MediaSessionUmaHelper();
-
-  void RecordSessionSuspended(MediaSessionSuspendedSource source) const;
-
-  // Record the result of calling the native requestAudioFocus().
-  void RecordRequestAudioFocusResult(bool result) const;
-
-  void OnSessionActive();
-  void OnSessionSuspended();
-  void OnSessionInactive();
-
-  void SetClockForTest(scoped_ptr<base::Clock> testing_clock);
-
- private:
-  base::TimeDelta total_active_time_;
-  base::Time current_active_time_;
-  scoped_ptr<base::Clock> clock_;
-};
-
-}  // namespace content
-
-#endif // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_UMA_HELPER_H_