[Presentation API] Change ListenForSessionMessages API to client-style.

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 7fd66fa4017a62531b7d508fd9043eab1f48f168..7405f4f28bc6d3d2c881fbfa0f742004f466d634 100644
--- a/chrome/browser/media/router/media_router.h
+++ b/chrome/browser/media/router/media_router.h
@@ -21,15 +21,25 @@ namespace media_router {
 class IssuesObserver;
 class MediaRoutesObserver;
 class MediaSinksObserver;
-
-// Type of callback used in |CreateRoute()|. Callback is invoked when the
-// route request either succeeded or failed.
-// The first argument is the route created. If the route request failed, this
-// will be a nullptr.
-// The second argument is the error string, which will be nonempty if the route
-// request failed.
+class PresentationSessionMessagesObserver;
+
+// Type of callback used in |CreateRoute()| and |JoinRoute()|. Callback is
+// invoked when the route request either succeeded or failed.
+// On success:
+// |route|: The route created or joined.
+// |presentation_id|:
+//     The presentation ID of the route created or joined. In the case of
+//     |CreateRoute()|, the ID is generated by MediaRouter and is guaranteed to
+//     be unique.
+// |error|: Empty string.
+// On failure:
+// |route|: nullptr
+// |presentation_id|: Empty string.
+// |error|: Non-empty string describing the error.
 using MediaRouteResponseCallback =
-    base::Callback<void(const MediaRoute*, const std::string&)>;
+    base::Callback<void(const MediaRoute* route,
+                        const std::string& presentation_id,
+                        const std::string& error)>;
 
 // Used in cases where a tab ID is not applicable in CreateRoute/JoinRoute.
 const int kInvalidTabId = -1;
@@ -93,14 +103,6 @@ class MediaRouter : public KeyedService {
       scoped_ptr<std::vector<uint8>> data,
       const SendRouteMessageCallback& callback) = 0;
 
-  // Gets the next batch of messages from one of the routes in |route_ids|.
-  // |message_cb|: Invoked with a non-empty list of messages when there are
-  //      messages, an empty list when messaging channel had error.
-  //      It is not invoked until there are messages available or error.
-  virtual void ListenForRouteMessages(
-      const std::vector<MediaRoute::Id>& route_ids,
-      const PresentationSessionMessageCallback& message_cb) = 0;
-
   // Clears the issue with the id |issue_id|.
   virtual void ClearIssue(const Issue::Id& issue_id) = 0;
 
@@ -108,9 +110,9 @@ class MediaRouter : public KeyedService {
   friend class IssuesObserver;
   friend class MediaSinksObserver;
   friend class MediaRoutesObserver;
+  friend class PresentationSessionMessagesObserver;
 
-  // The following functions are called by IssuesObserver, MediaSinksObserver,
-  // and MediaRoutesObserver.
+  // The following functions are called by friend Observer classes above.
 
   // Registers |observer| with this MediaRouter. |observer| specifies a media
   // source and will receive updates with media sinks that are compatible with
@@ -130,7 +132,7 @@ class MediaRouter : public KeyedService {
 
   // Adds a MediaRoutesObserver to listen for updates on MediaRoutes.
   // The initial update may happen synchronously.
-  // MediaRouter does not own |observer|. |RemoveMediaRoutesObserver| should
+  // MediaRouter does not own |observer|. |UnregisterMediaRoutesObserver| should
   // be called before |observer| is destroyed.
   // It is invalid to register the same observer more than once and will result
   // in undefined behavior.
@@ -147,6 +149,20 @@ class MediaRouter : public KeyedService {
 
   // Removes the IssuesObserver |observer|.
   virtual void UnregisterIssuesObserver(IssuesObserver* observer) = 0;
+
+  // Registers |observer| with this MediaRouter. |observer| specifies a media
+  // route corresponding to a presentation and will receive messages from the
+  // MediaSink connected to the route. Note that MediaRouter does not own
+  // |observer|. |observer| should be unregistered before it is destroyed.
+  // Registering the same observer more than once will result in undefined
+  // behavior.
+  virtual void RegisterPresentationSessionMessagesObserver(
+      PresentationSessionMessagesObserver* observer) = 0;
+
+  // Unregisters a previously registered PresentationSessionMessagesObserver.
+  // |observer| will stop receiving further updates.
+  virtual void UnregisterPresentationSessionMessagesObserver(
+      PresentationSessionMessagesObserver* observer) = 0;
 };
 
 }  // namespace media_router