Implement Audio Focus Manager for desktop.

content/browser/media/session/media_session_delegate_default.cc

Index: content/browser/media/session/media_session_delegate_default.cc
diff --git a/content/browser/media/session/media_session_delegate_default.cc b/content/browser/media/session/media_session_delegate_default.cc
index 688ce53d14f2743862310b10ae9d3c2286b72067..8a3db14fb2dc84a55ec612b4d849bd8f350ee0cc 100644
--- a/content/browser/media/session/media_session_delegate_default.cc
+++ b/content/browser/media/session/media_session_delegate_default.cc
@@ -5,11 +5,13 @@
 #include "content/browser/media/session/media_session_delegate.h"
 
 #include "base/command_line.h"
-#include "content/browser/web_contents/web_contents_impl.h"
+#include "content/browser/media/session/audio_focus_manager.h"
 #include "media/base/media_switches.h"
 
 namespace content {
 
+using AudioFocusType = AudioFocusManager::AudioFocusType;
+
 namespace {
 
 // MediaSessionDelegateDefault is the default implementation of
@@ -34,22 +36,21 @@ MediaSessionDelegateDefault::MediaSessionDelegateDefault(
     : media_session_(media_session) {
 }
 
-bool MediaSessionDelegateDefault::RequestAudioFocus(MediaSession::Type) {
+bool MediaSessionDelegateDefault::RequestAudioFocus(MediaSession::Type type) {
   if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableDefaultMediaSession)) {
     return true;
   }
 
-  for (WebContentsImpl* web_contents : WebContentsImpl::GetAllWebContents()) {
-    MediaSession* media_session = MediaSession::Get(web_contents);
-    if (media_session == media_session_ || !media_session->IsActive())
-      continue;
-    media_session->Suspend(MediaSession::SuspendType::SYSTEM);
-  }
+  AudioFocusManager::GetInstance()->RequestAudioFocus(
+      media_session_, type == MediaSession::Type::Content
+                          ? AudioFocusType::Gain
+                          : AudioFocusType::GainTransientMayDuck);
   return true;
 }
 
 void MediaSessionDelegateDefault::AbandonAudioFocus() {
+  AudioFocusManager::GetInstance()->AbandonAudioFocus(media_session_);
 }
 
 // static