Implement one-shot audio focus inside MediaSession

content/browser/media/session/media_session_impl.cc

Index: content/browser/media/session/media_session_impl.cc
diff --git a/content/browser/media/session/media_session_impl.cc b/content/browser/media/session/media_session_impl.cc
index 022efebc1331af527436b75cc650e019644d8266..bb6041d4bb0ec0ea1dd5ec7c3b466e660d488952 100644
--- a/content/browser/media/session/media_session_impl.cc
+++ b/content/browser/media/session/media_session_impl.cc
@@ -65,6 +65,8 @@ MediaSessionImpl* MediaSessionImpl::Get(WebContents* web_contents) {
 
 MediaSessionImpl::~MediaSessionImpl() {
   DCHECK(players_.empty());
+  DCHECK(pepper_players_.empty());
+  DCHECK(one_shot_players_.empty());
   DCHECK(audio_focus_state_ == State::INACTIVE);
   for (auto& observer : observers_)
     observer.MediaSessionDestroyed();
@@ -101,16 +103,13 @@ void MediaSessionImpl::SetMetadata(
 bool MediaSessionImpl::AddPlayer(MediaSessionPlayerObserver* observer,
                                  int player_id,
                                  media::MediaContentType media_content_type) {
-  if (media_content_type == media::MediaContentType::Uncontrollable)
-    return true;
+  if (media_content_type == media::MediaContentType::OneShot)
+    return AddOneShotPlayer(observer, player_id);
   if (media_content_type == media::MediaContentType::Pepper)
     return AddPepperPlayer(observer, player_id);
 
   observer->OnSetVolumeMultiplier(player_id, GetVolumeMultiplier());
 
-  // Determine the audio focus type required for playing the new player.
-  // TODO(zqzhang): handle duckable and uncontrollable.
-  // See https://crbug.com/639277.
   AudioFocusManager::AudioFocusType required_audio_focus_type;
   if (media_content_type == media::MediaContentType::Persistent) {
     required_audio_focus_type = AudioFocusManager::AudioFocusType::Gain;
@@ -142,7 +141,7 @@ bool MediaSessionImpl::AddPlayer(MediaSessionPlayerObserver* observer,
     players_.clear();
 
   players_.insert(PlayerIdentifier(observer, player_id));
-  UpdateWebContents();
+  DispatchStateChange();
 
   return true;
 }
@@ -157,6 +156,16 @@ void MediaSessionImpl::RemovePlayer(MediaSessionPlayerObserver* observer,
   if (it != pepper_players_.end())
     pepper_players_.erase(it);
 
+  it = one_shot_players_.find(PlayerIdentifier(observer, player_id));
+  if (it != one_shot_players_.end()) {
+    one_shot_players_.erase(it);
+
+    // The session may become controllable after all one-shot players are
+    // removed.
+    if (one_shot_players_.empty())
+      DispatchStateChange();
+  }
+
   AbandonSystemAudioFocusIfNeeded();
 }
 
@@ -175,6 +184,18 @@ void MediaSessionImpl::RemovePlayers(MediaSessionPlayerObserver* observer) {
       ++it;
   }
 
+  for (auto it = one_shot_players_.begin(); it != one_shot_players_.end();) {
+    if (it->observer == observer)
+      one_shot_players_.erase(it++);
+    else
+      ++it;
+
+    // The session may become controllable after all one-shot players are
+    // removed.
+    if (one_shot_players_.empty())
+      DispatchStateChange();
+  }
+
   AbandonSystemAudioFocusIfNeeded();
 }
 
@@ -191,7 +212,8 @@ void MediaSessionImpl::OnPlayerPaused(MediaSessionPlayerObserver* observer,
   // to this session (e.g. a silent video) is paused. MediaSessionImpl
   // should ignore the paused player for this case.
   if (!players_.count(PlayerIdentifier(observer, player_id)) &&
-      !pepper_players_.count(PlayerIdentifier(observer, player_id))) {
+      !pepper_players_.count(PlayerIdentifier(observer, player_id)) &&
+      !one_shot_players_.count(PlayerIdentifier(observer, player_id))) {
     return;
   }
 
@@ -203,6 +225,13 @@ void MediaSessionImpl::OnPlayerPaused(MediaSessionPlayerObserver* observer,
     return;
   }
 
+  // If the player is a one-shot player, just remove it since it is not expected
+  // to resume a one-shot player via resuming MediaSession.
+  if (one_shot_players_.count(PlayerIdentifier(observer, player_id))) {
+    RemovePlayer(observer, player_id);
+    return;
+  }
+
   // Otherwise, suspend the session.
   DCHECK(!IsSuspended());
   OnSuspendInternal(SuspendType::CONTENT, State::SUSPENDED);
@@ -294,9 +323,11 @@ bool MediaSessionImpl::IsSuspended() const {
 
 bool MediaSessionImpl::IsControllable() const {
   // Only media session having focus Gain can be controllable unless it is
-  // inactive.
+  // inactive. Also, the session will be uncontrollable if it contains one-shot
+  // players.
   return audio_focus_state_ != State::INACTIVE &&
-         audio_focus_type_ == AudioFocusManager::AudioFocusType::Gain;
+         audio_focus_type_ == AudioFocusManager::AudioFocusType::Gain &&
+         (one_shot_players_.empty());
 }
 
 bool MediaSessionImpl::HasPepper() const {
@@ -324,6 +355,8 @@ MediaSessionUmaHelper* MediaSessionImpl::uma_helper_for_test() {
 
 void MediaSessionImpl::RemoveAllPlayersForTest() {
   players_.clear();
+  pepper_players_.clear();
+  one_shot_players_.clear();

[whywhat, 2016/11/03 14:32:17]

nit: I feel there's more code duplication here w.r.t. three collections of
players

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

Yeah, I feel this too. But as pepper_players_ is likely to go away, let's keep
it here.

   AbandonSystemAudioFocusIfNeeded();
 }
 
@@ -335,6 +368,9 @@ void MediaSessionImpl::OnSuspendInternal(SuspendType suspend_type,
   // UI suspend cannot use State::INACTIVE.
   DCHECK(suspend_type == SuspendType::SYSTEM || new_state == State::SUSPENDED);
 
+  if (!one_shot_players_.empty())
+    return;
+
   if (audio_focus_state_ != State::ACTIVE)
     return;
 
@@ -376,7 +412,7 @@ void MediaSessionImpl::OnSuspendInternal(SuspendType suspend_type,
   for (const auto& it : pepper_players_)
     it.observer->OnSetVolumeMultiplier(it.player_id, kDuckingVolumeMultiplier);
 
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
 void MediaSessionImpl::OnResumeInternal(SuspendType suspend_type) {
@@ -391,7 +427,7 @@ void MediaSessionImpl::OnResumeInternal(SuspendType suspend_type) {
   for (const auto& it : pepper_players_)
     it.observer->OnSetVolumeMultiplier(it.player_id, GetVolumeMultiplier());
 
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
 MediaSessionImpl::MediaSessionImpl(WebContents* web_contents)
@@ -423,16 +459,16 @@ bool MediaSessionImpl::RequestSystemAudioFocus(
 
 void MediaSessionImpl::AbandonSystemAudioFocusIfNeeded() {
   if (audio_focus_state_ == State::INACTIVE || !players_.empty() ||
-      !pepper_players_.empty()) {
+      !pepper_players_.empty() || !one_shot_players_.empty()) {
     return;
   }
   delegate_->AbandonAudioFocus();
 
   SetAudioFocusState(State::INACTIVE);
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
-void MediaSessionImpl::UpdateWebContents() {
+void MediaSessionImpl::DispatchStateChange() {
   media_session_state_listeners_.Notify(audio_focus_state_);
   for (auto& observer : observers_)
     observer.MediaSessionStateChanged(IsControllable(), IsSuspended());
@@ -466,6 +502,19 @@ bool MediaSessionImpl::AddPepperPlayer(MediaSessionPlayerObserver* observer,
 
   observer->OnSetVolumeMultiplier(player_id, GetVolumeMultiplier());
 
+  DispatchStateChange();
+  return true;
+}
+
+bool MediaSessionImpl::AddOneShotPlayer(MediaSessionPlayerObserver* observer,
+                                        int player_id) {
+  // Don't check whether the request is successful or not. One-shot players
+  // should play uninterrupted.

[whywhat, 2016/11/03 14:32:16]

that means we'd play them even if the user is in the middle of a phone call? is
it intended?

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

OK, let's give a chance for the players to respond.

+  RequestSystemAudioFocus(AudioFocusManager::AudioFocusType::Gain);
+
+  one_shot_players_.insert(PlayerIdentifier(observer, player_id));
+
+  DispatchStateChange();
   return true;
 }