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..72e3b86e9f872f798a05b971ccb6433bd8aedc9e 100644
--- a/content/browser/media/session/media_session.cc
+++ b/content/browser/media/session/media_session.cc
@@ -5,12 +5,17 @@
 #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"
 #include "content/public/browser/web_contents_delegate.h"
 #include "media/base/media_content_type.h"
 
+#if defined(OS_ANDROID)
+#include "content/browser/media/session/media_session_android.h"
+#endif  // defined(OS_ANDROID
+
 namespace content {
 
 namespace {
@@ -57,6 +62,20 @@ MediaSession* MediaSession::Get(WebContents* web_contents) {
 MediaSession::~MediaSession() {
   DCHECK(players_.empty());
   DCHECK(audio_focus_state_ == State::INACTIVE);
+  for (auto& observer : observers_)
+    observer.MediaSessionDestroyed();
+#if defined(OS_ANDROID)
+  // Reset session_android to prevent further messages from Java.
+  session_android_.reset();
+#endif  // defined(OS_ANDROID)
+}
+
+void MediaSession::AddObserver(MediaSessionObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void MediaSession::RemoveObserver(MediaSessionObserver* observer) {
+  observers_.RemoveObserver(observer);
 }
 
 void MediaSession::WebContentsDestroyed() {
@@ -74,8 +93,9 @@ 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,
@@ -379,7 +399,11 @@ MediaSession::MediaSession(WebContents* web_contents)
       audio_focus_state_(State::INACTIVE),
       audio_focus_type_(
           AudioFocusManager::AudioFocusType::GainTransientMayDuck),
-      is_ducking_(false) {}
+      is_ducking_(false) {
+#if defined(OS_ANDROID)
+  session_android_.reset(new MediaSessionAndroid(this));
+#endif  // defined(OS_ANDROID)
+}
 
 void MediaSession::Initialize() {
   delegate_ = AudioFocusDelegate::Create(this);
@@ -410,7 +434,8 @@ 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) {