Reland "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..cad3c5e292356e3b977cf00304d58d56dadd6520 100644
--- a/content/browser/media/session/audio_focus_manager.cc
+++ b/content/browser/media/session/audio_focus_manager.cc
@@ -4,28 +4,12 @@
 
 #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"
 
 namespace content {
 
-AudioFocusManager::AudioFocusEntry::AudioFocusEntry(
-    WebContents* web_contents,
-    AudioFocusManager* audio_focus_manager,
-    AudioFocusType type)
-    : WebContentsObserver(web_contents),
-      audio_focus_manager_(audio_focus_manager) {}
-
-AudioFocusManager::AudioFocusType
-AudioFocusManager::AudioFocusEntry::type() const {
-  return type_;
-}
-
-void AudioFocusManager::AudioFocusEntry::WebContentsDestroyed() {
-  audio_focus_manager_->OnWebContentsDestroyed(web_contents());
-  // |this| will be destroyed now.
-}
-
 // static
 AudioFocusManager* AudioFocusManager::GetInstance() {
   return base::Singleton<AudioFocusManager>::get();
@@ -33,83 +17,77 @@ AudioFocusManager* AudioFocusManager::GetInstance() {
 
 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() == media_session &&
+      audio_focus_stack_.back()->audio_focus_type() == type &&
+      audio_focus_stack_.back()->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(media_session);
 
-    MediaSession* other_session =
-        MediaSession::Get(focus_entry_->web_contents());
-    if (other_session->IsActive())
-      other_session->Suspend(MediaSession::SuspendType::SYSTEM);
+  // TODO(zqzhang): It seems like MediaSession is exposed to AudioFocusManager
+  // too much. Maybe it's better to do some abstraction and refactoring to clean
+  // up the relation between AudioFocusManager and MediaSession.
+  // See https://crbug.com/651069
+  if (type == AudioFocusType::GainTransientMayDuck) {
+    for (const auto old_session : audio_focus_stack_) {
+      old_session->StartDucking();
+    }
+  } else {
+    for (const auto old_session : audio_focus_stack_) {
+      if (old_session->IsActive()) {
+        if (old_session->HasPepper())
+          old_session->StartDucking();
+        else
+          old_session->Suspend(MediaSession::SuspendType::SYSTEM);
+      }
+    }
   }
 
-  focus_entry_.reset(
-      new AudioFocusEntry(web_contents, this, AudioFocusType::Gain));
-  MaybeStartDucking();
-}
-
-void AudioFocusManager::OnWebContentsDestroyed(WebContents* web_contents) {
-  AbandonAudioFocusInternal(web_contents);
-}
-
-void AudioFocusManager::AbandonAudioFocusInternal(WebContents* web_contents) {
-  MaybeRemoveTransientEntry(web_contents);
-  MaybeRemoveFocusEntry(web_contents);
+  audio_focus_stack_.push_back(media_session);
+  audio_focus_stack_.back()->StopDucking();
 }
 
-void AudioFocusManager::MaybeStartDucking() const {
-  if (TransientMayDuckEntriesCount() != 1 || !focus_entry_)
+void AudioFocusManager::AbandonAudioFocus(MediaSession* media_session) {
+  if (audio_focus_stack_.empty())
     return;
 
-  MediaSession::Get(focus_entry_->web_contents())->StartDucking();
-}
+  if (audio_focus_stack_.back() != media_session) {
+    MaybeRemoveFocusEntry(media_session);
+    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)->HasPepper())
+      continue;
+
+    MediaSession* pepper_session = *iter;
+    pepper_session->StopDucking();
+    MaybeRemoveFocusEntry(pepper_session);
+    audio_focus_stack_.push_back(pepper_session);
+    return;
+  }
+  // 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()->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::MaybeRemoveFocusEntry(WebContents* web_contents) {
-  if (focus_entry_ && focus_entry_->web_contents() == web_contents) {
-    MediaSession::Get(focus_entry_->web_contents())->StopDucking();
-    focus_entry_.reset();
-  }
+void AudioFocusManager::MaybeRemoveFocusEntry(MediaSession* media_session) {
+  audio_focus_stack_.remove(media_session);
 }
 
 }  // namespace content