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

content/browser/media/android/media_session.h

Index: content/browser/media/android/media_session.h
diff --git a/content/browser/media/android/media_session.h b/content/browser/media/android/media_session.h
new file mode 100644
index 0000000000000000000000000000000000000000..f36bb4ef13d79f35abbb55269d149ea10be349a9
--- /dev/null
+++ b/content/browser/media/android/media_session.h
@@ -0,0 +1,134 @@
+// 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/common/content_export.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+namespace content {
+
+class MediaSessionBrowserTest;
+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 content::WebContentsObserver,
+      protected content::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, jobject obj, jboolean temporary);
+
+  // Called when the Android system requests the MediaSession to be resumed.
+  // Called by Java through JNI.
+  void OnResume(JNIEnv* env, jobject obj);
+
+ protected:
+  friend class content::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 OnSuspend(bool temporary);
+  void OnResume();
+
+ private:
+  friend class content::WebContentsUserData<MediaSession>;
+
+  enum class State {
+    Active,
+    TemporarilySuspended,
+    Suspended,
+  };
+
+  // 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();
+
+  // 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();
+
+  base::android::ScopedJavaGlobalRef<jobject> j_media_session_;
+  PlayersMap players_;
+
+  State audio_focus_state_;
+  Type audio_focus_type_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSession);
+};
+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_H_