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

chrome/browser/media/router/presentation_session_messages_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_session_messages_observer.h"
+
+#include "chrome/browser/media/router/media_router.h"
+
+namespace media_router {
+
+PresentationSessionMessagesObserver::PresentationSessionMessagesObserver(
+    const content::PresentationSessionMessageCallback& message_cb,
+    const MediaRoute::Id& route_id,
+    MediaRouter* router)
+    : message_cb_(message_cb), route_id_(route_id), router_(router) {
+  DCHECK(!message_cb_.is_null());
+  DCHECK(!route_id_.empty());
+  DCHECK(router_);
+  router_->RegisterPresentationSessionMessagesObserver(this);
+}
+
+PresentationSessionMessagesObserver::~PresentationSessionMessagesObserver() {
+  router_->UnregisterPresentationSessionMessagesObserver(this);
+}
+
+void PresentationSessionMessagesObserver::OnMessagesReceived(
+    const ScopedVector<content::PresentationSessionMessage>& messages) {
+  DVLOG(2) << __FUNCTION__ << ", number of messages : " << messages.size();
+  DCHECK(!messages.empty());
+  message_cb_.Run(messages);
+}
+
+}  // namespace media_router