Move audio focus control from media/ to content/ and make it per WebContents.

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 "base/android/scoped_java_ref.h"
+#include "base/id_map.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+namespace content {
+
+class MediaSessionDelegate;
+
+// 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.
+// It is communicating to the Android system trough MediaSession.java via JNI.
+class MediaSession : public content::WebContentsObserver,
+                     protected content::WebContentsUserData<MediaSession> {
+ public:
+  enum class Type {
+    Content,
+    Transient
+  };
+
+  static bool RegisterMediaSession(JNIEnv* env);
+
+  // Returns the MediaSession associated to this WebContents. Create 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(MediaSessionDelegate* delegate, int player_id, Type type);
+
+  // Removes the given player from the current media session. Abandon audio
+  // focus if that was the last player in the session.
+  void RemovePlayer(MediaSessionDelegate* delegate, int player_id);
+
+  // Removes all the players associated with |delegate|. Abandon audio focus if
+  // these were the last players in the session.
+  void RemovePlayers(MediaSessionDelegate* delegate);
+
+  // Called by Java trough JNI.
+  void OnSuspend(JNIEnv* env, jobject obj);
+  void OnResume(JNIEnv* env, jobject obj);
+
+ private:
+  friend class content::WebContentsUserData<MediaSession>;
+
+  // Representation of a player for the MediaSession.
+  struct PlayerIdentifier {
+    PlayerIdentifier(MediaSessionDelegate* delegate, 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;
+    };
+
+    MediaSessionDelegate* delegate;
+    int player_id;
+  };
+  using PlayersMap = base::hash_set<PlayerIdentifier, PlayerIdentifier::Hash>;
+
+  explicit MediaSession(WebContents* web_contents);
+
+  // Setup the JNI.
+  void Initialize();
+
+  // 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();
+
+  base::android::ScopedJavaGlobalRef<jobject> j_media_session_;
+  PlayersMap players_;
+
+  bool has_audio_focus_;
+  Type audio_focus_type_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSession);
+};
+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_H_