Link MediaSessionTabHelper with native MediaSession [CL is going to be split]

content/browser/media/session/media_session.cc

Index: content/browser/media/session/media_session.cc
diff --git a/content/browser/media/session/media_session.cc b/content/browser/media/session/media_session.cc
index ea25caad4df7d8adeb230f46523aa00d64e6c3d1..73b5f47941a18ac898cfb6d30aca2336fe402ef9 100644
--- a/content/browser/media/session/media_session.cc
+++ b/content/browser/media/session/media_session.cc
@@ -5,6 +5,7 @@
 #include "content/browser/media/session/media_session.h"
 
 #include "content/browser/media/session/audio_focus_delegate.h"
+#include "content/browser/media/session/media_session_observer.h"
 #include "content/browser/media/session/media_session_player_observer.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/web_contents.h"
@@ -57,6 +58,26 @@ MediaSession* MediaSession::Get(WebContents* web_contents) {
 MediaSession::~MediaSession() {
   DCHECK(players_.empty());
   DCHECK(audio_focus_state_ == State::INACTIVE);
+  owned_observers_.clear();

[whywhat, 2016/10/21 18:28:14]

I think MediaSession should notify MediaSessionObservers it's about to be
destroyed so they could set their session_ to nullptr.
It's not MediaSessionDelegate's responsibility.

[derekjchow1, 2016/10/21 20:47:30]

+1. This is the pattern used in WebContentsObserver.

https://cs.chromium.org/chromium/src/content/public/browser/web_contents_obse...

You could add a MediaSessionDestroyed function to MediaSessionObserver. This
notification would be sent out in the destructor of MediaSession.
MediaSessionDelegate can then "own itself" and delete itself when it gets that
notification. This way a PassObserverOwnership function is no longer needed.

+}
+
+void MediaSession::AddObserver(MediaSessionObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void MediaSession::RemoveObserver(MediaSessionObserver* observer) {
+  observers_.RemoveObserver(observer);
+  for (auto iter = owned_observers_.begin(); iter != owned_observers_.end();

[derekjchow1, 2016/10/21 20:47:30]

You could use std::find here.

+       ++iter) {
+    if (iter->get() == observer)
+      owned_observers_.erase(iter);
+    return;

[whywhat, 2016/10/21 18:28:14]

this return belongs to the if above

+  }
+}
+
+void MediaSession::PassObserverOwnership(
+    std::unique_ptr<MediaSessionObserver> observer) {
+  owned_observers_.push_back(std::move(observer));
 }
 
 void MediaSession::WebContentsDestroyed() {
@@ -74,8 +95,9 @@ void MediaSession::WebContentsDestroyed() {
 
 void MediaSession::SetMetadata(const base::Optional<MediaMetadata>& metadata) {
   metadata_ = metadata;
-  static_cast<WebContentsImpl*>(web_contents())
-      ->OnMediaSessionMetadataChanged();
+
+  for (auto& observer : observers_)
+    observer.MediaSessionMetadataChanged(metadata_);
 }
 
 bool MediaSession::AddPlayer(MediaSessionPlayerObserver* observer,
@@ -410,7 +432,8 @@ void MediaSession::AbandonSystemAudioFocusIfNeeded() {
 
 void MediaSession::UpdateWebContents() {
   media_session_state_listeners_.Notify(audio_focus_state_);
-  static_cast<WebContentsImpl*>(web_contents())->OnMediaSessionStateChanged();
+  for (auto& observer : observers_)
+    observer.MediaSessionStateChanged(IsControllable(), IsSuspended());
 }
 
 void MediaSession::SetAudioFocusState(State audio_focus_state) {