Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/session/mock_media_session_observer.h

Index: content/browser/media/session/mock_media_session_observer.h
diff --git a/content/browser/media/session/mock_media_session_observer.h b/content/browser/media/session/mock_media_session_observer.h
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+++ b/content/browser/media/session/mock_media_session_observer.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.
+
+#include <stddef.h>
+#include <vector>
+
+#include "content/browser/media/session/media_session_observer.h"
+
+namespace content {
+
+// MockMediaSessionObserver is a mock implementation of MediaSessionObserver to
+// be used in tests.
+class MockMediaSessionObserver : public MediaSessionObserver {
+ public:
+  MockMediaSessionObserver();
+  ~MockMediaSessionObserver() override;
+
+  // Implements MediaSessionObserver.
+  void OnSuspend(int player_id) override;
+  void OnResume(int player_id) override;
+  void OnSetVolumeMultiplier(int player_id, double volume_multiplier) override;
+
+  // Simulate that a new player started.
+  // Returns the player_id.
+  int StartNewPlayer();
+
+  // Returns whether |player_id| is playing.
+  bool IsPlaying(size_t player_id);
+
+  // Returns the volume multiplier of |player_id|.
+  double GetVolumeMultiplier(size_t player_id);
+
+  // Simulate a play state change for |player_id|.
+  void SetPlaying(size_t player_id, bool playing);
+
+  int received_suspend_calls() const;
+  int received_resume_calls() const;
+
+ private:
+  // Internal representation of the players to keep track of their statuses.
+  struct MockPlayer {
+   public:
+    MockPlayer(bool is_playing = true, double volume_multiplier = 1.0f)
+        : is_playing_(is_playing),
+          volume_multiplier_(volume_multiplier) {}
+    bool is_playing_;
+    double volume_multiplier_;
+  };
+
+  // Basic representation of the players. The position in the vector is the
+  // player_id. The value of the vector is the playing status and volume.
+  std::vector<MockPlayer> players_;
+
+  int received_resume_calls_ = 0;
+  int received_suspend_calls_ = 0;
+};
+
+}  // namespace content