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..e92a2369f371f27226e4191b2cf8564b4f4860cd 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"
 
@@ -14,7 +15,8 @@ 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 {
@@ -35,80 +37,68 @@ 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)

[whywhat, 2016/09/07 20:09:54]

nit: use {} as the condition statement doesn't fit on one line.

[Zhiqiang Zhang (Slow), 2016/09/08 14:18:26]

Done.

     return;

[whywhat, 2016/09/07 20:09:54]

don't you need to check that the AudioFocusType is already the same?
could't you check audio_focus_stack_.back() == media_session?

[Zhiqiang Zhang (Slow), 2016/09/08 14:18:26]

Done.

-  }
-
-  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_) {
+      MediaSession::Get(focus_entry->web_contents())->StartDucking();
+    }
+  } else {
+    for (const auto& focus_entry : audio_focus_stack_) {
+      MediaSession* session = MediaSession::Get(focus_entry->web_contents());
+      if (session->IsActive())
+        session->Suspend(MediaSession::SuspendType::SYSTEM);
+    }
+  }
+  if (!audio_focus_stack_.empty()) {
+    MediaSession::Get(audio_focus_stack_.back()->web_contents())

[whywhat, 2016/09/07 20:09:54]

shouldn't Suspend or StartDucking do that? I feel that is_on_top_ will never be
true if the session is ducking or suspended so maybe it could be eliminated
altogether.

[Zhiqiang Zhang (Slow), 2016/09/08 14:18:26]

I'm renaming the flag `is_on_top_` to `allow_pepper_override_ducking`, and moved
this statement to the for-loop above.

The flag now indicates whether Pepper should unduck even if the session is
suspended/inactive.

+        ->SetOnTop(false);
   }
 
-  focus_entry_.reset(
-      new AudioFocusEntry(web_contents, this, AudioFocusType::Gain));
-  MaybeStartDucking();
-}
-
-void AudioFocusManager::OnWebContentsDestroyed(WebContents* web_contents) {
-  AbandonAudioFocusInternal(web_contents);
+  audio_focus_stack_.push_back(base::MakeUnique<AudioFocusEntry>(
+    web_contents, this, type));
+  MediaSession::Get(audio_focus_stack_.back()->web_contents())->StopDucking();

[whywhat, 2016/09/07 20:09:54]

How do we know it's not suspended but ducking?

[Zhiqiang Zhang (Slow), 2016/09/08 14:18:26]

If it's suspended, then this will be no-op, since we will not change the
suspended state.

+  MediaSession::Get(audio_focus_stack_.back()->web_contents())->SetOnTop(true);
 }
 
-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_.back()->web_contents() != web_contents) {
+    MaybeRemoveFocusEntry(web_contents);
     return;
+  }
 
-  MediaSession::Get(focus_entry_->web_contents())->StartDucking();
-}
-
-void AudioFocusManager::MaybeStopDucking() const {
-  if (TransientMayDuckEntriesCount() != 0 || !focus_entry_)
+  MediaSession::Get(audio_focus_stack_.back()->web_contents())->SetOnTop(false);
+  audio_focus_stack_.pop_back();
+  if (audio_focus_stack_.empty())
     return;
 
-  MediaSession::Get(focus_entry_->web_contents())->StopDucking();
+  MediaSession::Get(audio_focus_stack_.back()->web_contents())->SetOnTop(true);
+  // Only try to unduck the new MediaSession on top. The session might be still
+  // inactive but it will not be resumed (so it does surprise the user).
+  MediaSession::Get(audio_focus_stack_.back()->web_contents())->StopDucking();
 }
 
-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;
+    }
   }
 }