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..82370a16575175451ef9cfc90b0765fd48729198
--- /dev/null
+++ b/content/browser/media/android/media_session.h
@@ -0,0 +1,80 @@
+// 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

[whywhat, 2015/05/12 12:50:45]

I believe a more expanded comment would be welcome here.

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

Done.

+// requesting the audio focus, pausing when requested by the system and dropping
+// it on demand.
+class MediaSession : public content::WebContentsObserver,

[qinmin, 2015/05/15 18:06:19]

Can we merge this class with MediaWebContentsObserver? They are both observing
all media elements inside a webcontent, and holding a map of manager or player.

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

They are not quite doing the same thing. MediaSession has a map of active
players, part of the session. MediaWebContentsObserver has a map of
MediaPlayerManagers associated to each RenderFrameHost in a WebContents. Merging
them will be very odd and might just create a big class that would do two
different things.

+                     protected content::WebContentsUserData<MediaSession> {
+ public:
+  enum class Type {
+    Content,
+    Transient
+  };
+
+  static bool RegisterMediaSession(JNIEnv* env);
+  static MediaSession* Get(WebContents* web_contents);
+
+  ~MediaSession() override;
+
+  bool RequestAudioFocus(MediaSessionDelegate* delegate,

[whywhat, 2015/05/12 12:50:45]

Document the public methods.

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

Done.

+                         int player_id,

[whywhat, 2015/05/12 12:50:45]

This sounds more like "EnsureSufficientAudioFocus" because it only requests it
under some circumstances.
Or even CanPlayerPlay() to avoid exposing the audio focus to the users of the
class?

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

Renamed AddPlayer(). I changed how things behave to not add to the players_ list
if the audio focus isn't granted.

+                         Type type);
+  void AbandonAudioFocus(MediaSessionDelegate* delegate,

[whywhat, 2015/05/12 12:50:46]

Could be OnPlayerStopped then if you accept the suggestion above?

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

Renamed RemovePlayer(). OnPlayerStopped() is confusing given that we call it in
OnPause(). RemovePlayer() makes it clear that the player is removed from the
session.

+                         int player_id);
+  void AbandonAudioFocus(MediaSessionDelegate* delegate);

[whywhat, 2015/05/12 12:50:46]

Ditto. OnAllPlayersStopped() maybe?

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

RemovePlayers()

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

RemovePlayers()

+
+  // Called by Java trough JNI.
+  void OnSuspend(JNIEnv* env, jobject obj);
+  void OnResume(JNIEnv* env, jobject obj);
+
+ private:
+  friend class content::WebContentsUserData<MediaSession>;
+
+  struct PlayerIdentifier {
+    PlayerIdentifier(MediaSessionDelegate* delegate, int id)
+        : delegate_(delegate),
+          id_(id) {};
+    MediaSessionDelegate* delegate_;
+    int id_;
+
+    DISALLOW_COPY_AND_ASSIGN(PlayerIdentifier);

[whywhat, 2015/05/12 12:50:46]

nit: is it common for structs? not sure if this is common.

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

AFAIK, it is recommended if not required.

+  };
+  using PlayersMap = IDMap<PlayerIdentifier, IDMapOwnPointer>;
+
+  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 AbandonAudioFocusIfNeeded();

[whywhat, 2015/05/12 12:50:45]

s/AbandonAudioFocus/AbandonSystemAudioFocus?

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

Done.

+
+  base::android::ScopedJavaGlobalRef<jobject> j_media_session_;
+  PlayersMap players_;
+
+  bool has_audio_focus_;

[whywhat, 2015/05/12 12:50:46]

Add None to Type and just have one three-state member?

[mlamouri (slow - plz ping), 2015/05/19 21:56:16]

When ::OnResume() is called, the boolean is toggled back to true. To have the
same behaviour with a tree state, we would need to save the previous value,
which would be actually more expensive memory-wise. 

+  Type audio_focus_type_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSession);
+};
+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_H_