Reland "Adding media controls to MediaNotification"

content/public/browser/media_session_observer.h

Index: content/public/browser/media_session_observer.h
diff --git a/content/public/browser/media_session_observer.h b/content/public/browser/media_session_observer.h
index adfeeb0a672d1e42cc9a07599e993e07760ebb21..781c65a52f94a4aca759eb5f2735b5d6fa968f98 100644
--- a/content/public/browser/media_session_observer.h
+++ b/content/public/browser/media_session_observer.h
@@ -10,6 +10,12 @@
 #include "content/common/content_export.h"
 #include "content/public/common/media_metadata.h"
 
+namespace blink {
+namespace mojom {
+enum class MediaSessionAction;
+}  // namespace mojom
+}  // namespace blink
+
 namespace content {
 
 class MediaSession;
@@ -35,6 +41,14 @@ class CONTENT_EXPORT MediaSessionObserver {
   virtual void MediaSessionMetadataChanged(
       const base::Optional<MediaMetadata>& metadata) {}
 
+  // Called when media session action is enabled.
+  virtual void MediaSessionEnabledAction(
+      blink::mojom::MediaSessionAction action) {}
+
+  // Called when media session action is disabled.
+  virtual void MediaSessionDisabledAction(
+      blink::mojom::MediaSessionAction action) {}
+
  protected:
   // Create a MediaSessionObserver and start observing a session.
   MediaSessionObserver(MediaSession* media_session);