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

chrome/browser/media/router/presentation_connection_state_observer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/media/router/presentation_connection_state_observer.h"
 
 #include "base/logging.h"
 #include "chrome/browser/media/router/media_router.h"
 
 namespace media_router {
 
 PresentationConnectionStateObserver::PresentationConnectionStateObserver(
-    MediaRouter* router,
-    const MediaRoute::Id& route_id)
-    : router_(router), route_id_(route_id) {
+    const content::PresentationConnectionStateChangedCallback& state_changed_cb,
+    const content::PresentationSessionInfo& connection,
+    const MediaRoute::Id& route_id,
+    MediaRouter* router)
+    : state_changed_cb_(state_changed_cb),
+      connection_(connection),
+      route_id_(route_id),
+      router_(router) {
+  DCHECK(!state_changed_cb_.is_null());
   DCHECK(router_);
   router_->RegisterPresentationConnectionStateObserver(this);
 }
 
 PresentationConnectionStateObserver::~PresentationConnectionStateObserver() {
   router_->UnregisterPresentationConnectionStateObserver(this);
 }
 
+void PresentationConnectionStateObserver::OnStateChanged(
+    content::PresentationConnectionState state) {
+  DVLOG(2) << __FUNCTION__ << "presentation_id: " << connection_.presentation_id
+           << ", state: " << state;
+  state_changed_cb_.Run(connection_, state);

[mark a. foltz, 2015/11/12 04:19:38]

All this observer object is doing is wrapping a base::Callback.  What is the
advantage over adding an API to the media router,

router->RegisterPresentationConnectionStateCallback(route_id, connection,
state_changed_cb)

?

[imcheng, 2015/11/16 23:52:01]

If we pass in a callback, the implementation will use base::CallbackList and
Subscription objects. It will be different from the rest of the APIs in that
there won't a Unregister method, but it might be cleaner. I will give the
callback based API a try.

+}
+
 }  // namespace media_router