[Media Router] Connection state change listening redesign part 2.

chrome/browser/media/router/media_router.h

Index: chrome/browser/media/router/media_router.h
diff --git a/chrome/browser/media/router/media_router.h b/chrome/browser/media/router/media_router.h
index ed6cf1e80db026287f3c698092ef9c1517c8e089..14086bf4d0a1aae7ab8cf83dc7e978af71f36e93 100644
--- a/chrome/browser/media/router/media_router.h
+++ b/chrome/browser/media/router/media_router.h
@@ -9,12 +9,14 @@
 #include <vector>
 
 #include "base/callback.h"
+#include "base/callback_list.h"
 #include "base/memory/scoped_vector.h"
 #include "chrome/browser/media/router/issue.h"
 #include "chrome/browser/media/router/media_route.h"
 #include "chrome/browser/media/router/media_sink.h"
 #include "chrome/browser/media/router/media_source.h"
 #include "components/keyed_service/core/keyed_service.h"
+#include "content/public/browser/presentation_service_delegate.h"
 #include "content/public/browser/presentation_session_message.h"
 
 namespace content {
@@ -48,6 +50,12 @@ using MediaRouteResponseCallback =
                         const std::string& presentation_id,
                         const std::string& error)>;
 
+// Subscription object returned by calling
+// |AddPresentationConnectionStateChangedCallback|. See the method comments for
+// details.
+using PresentationConnectionStateSubscription = base::CallbackList<void(
+    content::PresentationConnectionState)>::Subscription;
+
 // An interface for handling resources related to media routing.
 // Responsible for registering observers for receiving sink availability
 // updates, handling route requests/responses, and operating on routes (e.g.
@@ -122,6 +130,14 @@ class MediaRouter : public KeyedService {
   // route.
   virtual bool HasLocalDisplayRoute() const = 0;
 
+  // Adds |callback| to listen for state changes for presentation connected to
+  // |route_id|. Callback will be invoked whenever there are state changes,
+  // until the returned Subscription object is destroyed.
+  virtual scoped_ptr<PresentationConnectionStateSubscription>
+  AddPresentationConnectionStateChangedCallback(
+      const MediaRoute::Id& route_id,
+      const content::PresentationConnectionStateChangedCallback& callback) = 0;
+
  private:
   friend class IssuesObserver;
   friend class LocalMediaRoutesObserver;
@@ -192,15 +208,6 @@ class MediaRouter : public KeyedService {
   // Removes the LocalMediaRoutesObserver |observer|.
   virtual void UnregisterLocalMediaRoutesObserver(
       LocalMediaRoutesObserver* observer) = 0;
-
-  // Registers/unregisters a PresentationConnectionStateObserver to receive
-  // updates on state changes for a PresentationConnection. MediaRouter does
-  // not own |observer|. When |observer| is about to be destroyed, it must be
-  // unregistered from MediaRouter.
-  virtual void RegisterPresentationConnectionStateObserver(
-      PresentationConnectionStateObserver* observer) = 0;
-  virtual void UnregisterPresentationConnectionStateObserver(
-      PresentationConnectionStateObserver* observer) = 0;
 };
 
 }  // namespace media_router