Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/media_web_contents_observer.cc

Index: content/browser/media/media_web_contents_observer.cc
diff --git a/content/browser/media/media_web_contents_observer.cc b/content/browser/media/media_web_contents_observer.cc
index 1123974df7b63597f042420cbbd1bdb681a89175..308451a9b6a26fbacb2ab1b5f34ef19b56a69845 100644
--- a/content/browser/media/media_web_contents_observer.cc
+++ b/content/browser/media/media_web_contents_observer.cc
@@ -26,7 +26,8 @@ static base::LazyInstance<AudibleMetrics>::Leaky g_audible_metrics =
 }  // anonymous namespace
 
 MediaWebContentsObserver::MediaWebContentsObserver(WebContents* web_contents)
-    : WebContentsObserver(web_contents) {}
+    : WebContentsObserver(web_contents),
+      session_controllers_manager_(this) {}
 
 MediaWebContentsObserver::~MediaWebContentsObserver() {}
 
@@ -37,6 +38,7 @@ void MediaWebContentsObserver::WebContentsDestroyed() {
 void MediaWebContentsObserver::RenderFrameDeleted(
     RenderFrameHost* render_frame_host) {
   ClearPowerSaveBlockers(render_frame_host);
+  session_controllers_manager_.Clear(render_frame_host);
 }
 
 void MediaWebContentsObserver::MaybeUpdateAudibleState() {
@@ -93,7 +95,6 @@ void MediaWebContentsObserver::OnMediaDestroyed(
   OnMediaPaused(render_frame_host, delegate_id, true);
 }
 
-
 void MediaWebContentsObserver::OnMediaPaused(RenderFrameHost* render_frame_host,
                                              int delegate_id,
                                              bool reached_end_of_stream) {
@@ -106,6 +107,11 @@ void MediaWebContentsObserver::OnMediaPaused(RenderFrameHost* render_frame_host,
     // Notify observers the player has been "paused".
     static_cast<WebContentsImpl*>(web_contents())->MediaStoppedPlaying(id);
   }
+
+  if (reached_end_of_stream)
+    session_controllers_manager_.OnEnd(id);
+  else
+    session_controllers_manager_.OnPause(id);
 }
 
 void MediaWebContentsObserver::OnMediaPlaying(
@@ -143,6 +149,11 @@ void MediaWebContentsObserver::OnMediaPlaying(
     }
   }
 
+  if (!session_controllers_manager_.RequestPlay(
+      id, has_audio, is_remote, duration)) {
+    return;
+  }
+
   // Notify observers of the new player.
   DCHECK(has_audio || has_video);
   static_cast<WebContentsImpl*>(web_contents())->MediaStartedPlaying(id);