Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/android/media_session.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_H_
-#define CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_H_
-
-#include <jni.h>
-#include <stddef.h>
-
-#include "base/android/scoped_java_ref.h"
-#include "base/id_map.h"
-#include "base/macros.h"
-#include "content/browser/media/android/media_session_uma_helper.h"
-#include "content/common/content_export.h"
-#include "content/public/browser/web_contents_observer.h"
-#include "content/public/browser/web_contents_user_data.h"
-
-class MediaSessionBrowserTest;
-
-namespace content {
-
-class MediaSessionObserver;
-
-// MediaSession manages the Android AudioFocus for a given WebContents. It is
-// requesting the audio focus, pausing when requested by the system and dropping
-// it on demand.
-// The audio focus can be of two types: Transient or Content. A Transient audio
-// focus will allow other players to duck instead of pausing and will be
-// declared as temporary to the system. A Content audio focus will not be
-// declared as temporary and will not allow other players to duck. If a given
-// WebContents can only have one audio focus at a time, it will be Content in
-// case of Transient and Content audio focus are both requested.
-// Android system interaction occurs in the Java counterpart to this class.
-class CONTENT_EXPORT MediaSession
-    : public WebContentsObserver,
-      protected WebContentsUserData<MediaSession> {
- public:
-  enum class Type {
-    Content,
-    Transient
-  };
-
-  static bool RegisterMediaSession(JNIEnv* env);
-
-  // Returns the MediaSession associated to this WebContents. Creates one if
-  // none is currently available.
-  static MediaSession* Get(WebContents* web_contents);
-
-  ~MediaSession() override;
-
-  // Adds the given player to the current media session. Returns whether the
-  // player was successfully added. If it returns false, AddPlayer() should be
-  // called again later.
-  bool AddPlayer(MediaSessionObserver* observer, int player_id, Type type);
-
-  // Removes the given player from the current media session. Abandons audio
-  // focus if that was the last player in the session.
-  void RemovePlayer(MediaSessionObserver* observer, int player_id);
-
-  // Removes all the players associated with |observer|. Abandons audio focus if
-  // these were the last players in the session.
-  void RemovePlayers(MediaSessionObserver* observer);
-
-  // Called when the Android system requests the MediaSession to be suspended.
-  // Called by Java through JNI.
-  void OnSuspend(JNIEnv* env,
-                 const base::android::JavaParamRef<jobject>& obj,
-                 jboolean temporary);
-
-  // Called when the Android system requests the MediaSession to duck.
-  // Called by Java through JNI.
-  void OnSetVolumeMultiplier(JNIEnv* env, jobject obj,
-                             jdouble volume_multiplier);
-
-  // Called when the Android system requests the MediaSession to be resumed.
-  // Called by Java through JNI.
-  void OnResume(JNIEnv* env, const base::android::JavaParamRef<jobject>& obj);
-
-  // Called when the Android system requests the MediaSession to duck.
-  // Called by Java through JNI.
-  void RecordSessionDuck(JNIEnv* env,
-                         const base::android::JavaParamRef<jobject> &obj);
-
-  // Called when a player is paused in the content.
-  // If the paused player is the last player, we suspend the MediaSession.
-  // Otherwise, the paused player will be removed from the MediaSession.
-  void OnPlayerPaused(MediaSessionObserver* observer, int player_id);
-
-  // Called when the user requests resuming the session. No-op if the session is
-  // not controllable.
-  void Resume();
-
-  // Called when the user requests suspending the session. No-op if the session
-  // is not controllable.
-  void Suspend();
-
-  // Called when the user requests stopping the session.
-  void Stop();
-
-  // Returns if the session can be controlled by Resume() and Suspend calls
-  // above.
-  bool IsControllable() const;
-
-  // Returns if the session is currently suspended.
-  bool IsSuspended() const;
-
- private:
-  friend class content::WebContentsUserData<MediaSession>;
-  friend class ::MediaSessionBrowserTest;
-
-  // Resets the |j_media_session_| ref to prevent calling the Java backend
-  // during content_browsertests.
-  void ResetJavaRefForTest();
-  bool IsActiveForTest() const;
-  Type audio_focus_type_for_test() const;
-  void RemoveAllPlayersForTest();
-  MediaSessionUmaHelper* uma_helper_for_test();
-
-  enum class State {
-    ACTIVE,
-    SUSPENDED,
-    INACTIVE
-  };
-
-  enum class SuspendType {
-    // Suspended by the system because a transient sound needs to be played.
-    SYSTEM,
-    // Suspended by the UI.
-    UI,
-    // Suspended by the page via script or user interaction.
-    CONTENT,
-  };
-
-  // Representation of a player for the MediaSession.
-  struct PlayerIdentifier {
-    PlayerIdentifier(MediaSessionObserver* observer, int player_id);
-    PlayerIdentifier(const PlayerIdentifier&) = default;
-
-    void operator=(const PlayerIdentifier&) = delete;
-    bool operator==(const PlayerIdentifier& player_identifier) const;
-
-    // Hash operator for base::hash_map<>.
-    struct Hash {
-      size_t operator()(const PlayerIdentifier& player_identifier) const;
-    };
-
-    MediaSessionObserver* observer;
-    int player_id;
-  };
-  using PlayersMap = base::hash_set<PlayerIdentifier, PlayerIdentifier::Hash>;
-
-  explicit MediaSession(WebContents* web_contents);
-
-  // Setup the JNI.
-  void Initialize();
-
-  void OnSuspendInternal(SuspendType type, State new_state);
-  void OnResumeInternal(SuspendType type);
-  void OnSetVolumeMultiplierInternal(double volume_multiplier);
-
-  // Requests audio focus to Android using |j_media_session_|.
-  // Returns whether the request was granted. If |j_media_session_| is null, it
-  // will always return true.
-  bool RequestSystemAudioFocus(Type type);
-
-  // To be called after a call to AbandonAudioFocus() in order to call the Java
-  // MediaSession if the audio focus really need to be abandoned.
-  void AbandonSystemAudioFocusIfNeeded();
-
-  // Notifies WebContents about the state change of the media session.
-  void UpdateWebContents();
-
-  // Internal method that should be used instead of setting audio_focus_state_.
-  // It sets audio_focus_state_ and notifies observers about the state change.
-  void SetAudioFocusState(State audio_focus_state);
-
-  base::android::ScopedJavaGlobalRef<jobject> j_media_session_;
-  PlayersMap players_;
-
-  State audio_focus_state_;
-  SuspendType suspend_type_;
-  Type audio_focus_type_;
-
-  MediaSessionUmaHelper uma_helper_;
-
-  // The volume multiplier of this session. All players in this session should
-  // multiply their volume with this multiplier to get the effective volume.
-  double volume_multiplier_;
-
-  DISALLOW_COPY_AND_ASSIGN(MediaSession);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_H_