Letting Flash join MediaSession (stack implementaion)

content/browser/media/session/audio_focus_manager.cc

Index: content/browser/media/session/audio_focus_manager.cc
diff --git a/content/browser/media/session/audio_focus_manager.cc b/content/browser/media/session/audio_focus_manager.cc
index 4ff3491de482542efe4781d46d153e896df8eef4..95cba347ab83dc72d5594513bd896db2afc6ef7e 100644
--- a/content/browser/media/session/audio_focus_manager.cc
+++ b/content/browser/media/session/audio_focus_manager.cc
@@ -4,6 +4,7 @@
 
 #include "content/browser/media/session/audio_focus_manager.h"
 
+#include "base/memory/ptr_util.h"
 #include "content/browser/media/session/media_session.h"
 #include "content/public/browser/web_contents.h"
 
@@ -14,13 +15,18 @@ AudioFocusManager::AudioFocusEntry::AudioFocusEntry(
     AudioFocusManager* audio_focus_manager,
     AudioFocusType type)
     : WebContentsObserver(web_contents),
-      audio_focus_manager_(audio_focus_manager) {}
+      audio_focus_manager_(audio_focus_manager),
+      type_(type) {}
 
 AudioFocusManager::AudioFocusType
 AudioFocusManager::AudioFocusEntry::type() const {
   return type_;
 }
 
+MediaSession* AudioFocusManager::AudioFocusEntry::GetMediaSession() const {
+  return MediaSession::Get(web_contents());
+}
+
 void AudioFocusManager::AudioFocusEntry::WebContentsDestroyed() {
   audio_focus_manager_->OnWebContentsDestroyed(web_contents());
   // |this| will be destroyed now.
@@ -35,80 +41,82 @@ void AudioFocusManager::RequestAudioFocus(MediaSession* media_session,
                                           AudioFocusType type) {
   WebContents* web_contents = media_session->web_contents();
 
-  if (type == AudioFocusType::GainTransientMayDuck) {
-    MaybeRemoveFocusEntry(web_contents);
-    transient_entries_[web_contents].reset(
-        new AudioFocusEntry(web_contents, this, type));
-    MaybeStartDucking();
+  if (!audio_focus_stack_.empty() &&
+      audio_focus_stack_.back()->web_contents() == web_contents &&
+      audio_focus_stack_.back()->type() == type &&
+      audio_focus_stack_.back()->GetMediaSession()->IsActive()) {
+    // Early returning if |media_session| is already on top (has focus) and is
+    // active.
     return;
   }
 
-  DCHECK(type == AudioFocusType::Gain);
-  RequestAudioFocusGain(web_contents);
-}
-
-void AudioFocusManager::AbandonAudioFocus(MediaSession* media_session) {
-  AbandonAudioFocusInternal(media_session->web_contents());
-}
-
-AudioFocusManager::AudioFocusManager() = default;
-
-AudioFocusManager::~AudioFocusManager() = default;
-
-void AudioFocusManager::RequestAudioFocusGain(WebContents* web_contents) {
-  MaybeRemoveTransientEntry(web_contents);
-
-  if (focus_entry_) {
-    if (focus_entry_->web_contents() == web_contents)
-      return;
+  MaybeRemoveFocusEntry(web_contents);
 
-    MediaSession* other_session =
-        MediaSession::Get(focus_entry_->web_contents());
-    if (other_session->IsActive())
-      other_session->Suspend(MediaSession::SuspendType::SYSTEM);
+  if (type == AudioFocusType::GainTransientMayDuck) {
+    for (const auto& focus_entry : audio_focus_stack_) {
+      focus_entry->GetMediaSession()->StartDucking();

[whywhat, 2016/09/27 17:54:16]

I think it's still cleaner if we just do something like:

for (const auto& focus_entry : audio_focus_stack_) {
  focus_entry->GetMediaSession()->LostAudioFocusTo(type);
}

MediaSession::LostAudioFocusTo(type) {
  if (type == MayDuck) {
    StartDucking();
    return;
  }

  if (!IsActive())
    return;

  if (HasPepper())
     StartDucking();
  else
     Suspend(SYSTEM);
}

This decouples MediaSession from AFM much better than moving all logic into AFM
and using MS as a struct with states...

[Zhiqiang Zhang (Slow), 2016/09/28 16:12:17]

Added TODO.

+    }
+  } else {
+    for (const auto& focus_entry : audio_focus_stack_) {
+      MediaSession* session = focus_entry->GetMediaSession();
+      if (session->IsActive()) {
+        if (session->HasPepper())
+          session->StartDucking();
+        else
+          session->Suspend(MediaSession::SuspendType::SYSTEM);
+      }
+    }
   }
 
-  focus_entry_.reset(
-      new AudioFocusEntry(web_contents, this, AudioFocusType::Gain));
-  MaybeStartDucking();
+  audio_focus_stack_.push_back(base::MakeUnique<AudioFocusEntry>(
+    web_contents, this, type));
+  audio_focus_stack_.back()->GetMediaSession()->StopDucking();
 }
 
-void AudioFocusManager::OnWebContentsDestroyed(WebContents* web_contents) {
-  AbandonAudioFocusInternal(web_contents);
-}
-
-void AudioFocusManager::AbandonAudioFocusInternal(WebContents* web_contents) {
-  MaybeRemoveTransientEntry(web_contents);
-  MaybeRemoveFocusEntry(web_contents);
-}
+void AudioFocusManager::AbandonAudioFocus(MediaSession* media_session) {
+  WebContents* web_contents = media_session->web_contents();
 
-void AudioFocusManager::MaybeStartDucking() const {
-  if (TransientMayDuckEntriesCount() != 1 || !focus_entry_)
+  if (audio_focus_stack_.empty())
     return;
 
-  MediaSession::Get(focus_entry_->web_contents())->StartDucking();
-}
+  if (audio_focus_stack_.back()->web_contents() != web_contents) {
+    MaybeRemoveFocusEntry(web_contents);
+    return;
+  }
 
-void AudioFocusManager::MaybeStopDucking() const {
-  if (TransientMayDuckEntriesCount() != 0 || !focus_entry_)
+  audio_focus_stack_.pop_back();
+  if (audio_focus_stack_.empty())
     return;
 
-  MediaSession::Get(focus_entry_->web_contents())->StopDucking();
+  // Allow the top-most MediaSession having Pepper to unduck pepper even if it's
+  // not active.
+  for (auto iter = audio_focus_stack_.rbegin();
+       iter != audio_focus_stack_.rend(); ++iter) {
+    if ((*iter)->GetMediaSession()->HasPepper()) {
+      (*iter)->GetMediaSession()->StopDucking();
+      break;
+    }
+  }
+  // Only try to unduck the new MediaSession on top. The session might be still
+  // inactive but it will not be resumed (so it doesn't surprise the user).
+  audio_focus_stack_.back()->GetMediaSession()->StopDucking();

[whywhat, 2016/09/27 17:54:16]

Wouldn't you call StopDucking twice if the top MS has pepper?

[Zhiqiang Zhang (Slow), 2016/09/28 16:12:17]

s/break/return/ in line 97.

 }
 
-int AudioFocusManager::TransientMayDuckEntriesCount() const {
-  return transient_entries_.size();
-}
+AudioFocusManager::AudioFocusManager() = default;
 
-void AudioFocusManager::MaybeRemoveTransientEntry(WebContents* web_contents) {
-  transient_entries_.erase(web_contents);
-  MaybeStopDucking();
+AudioFocusManager::~AudioFocusManager() = default;
+
+void AudioFocusManager::OnWebContentsDestroyed(WebContents* web_contents) {
+  AbandonAudioFocus(MediaSession::Get(web_contents));
 }
 
 void AudioFocusManager::MaybeRemoveFocusEntry(WebContents* web_contents) {
-  if (focus_entry_ && focus_entry_->web_contents() == web_contents) {
-    MediaSession::Get(focus_entry_->web_contents())->StopDucking();
-    focus_entry_.reset();
+  for (auto iter = audio_focus_stack_.begin(); iter != audio_focus_stack_.end();
+       ++iter) {
+    if (web_contents == (*iter)->web_contents()) {
+      audio_focus_stack_.erase(iter);
+      return;
+    }
   }
 }