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

chrome/browser/media/router/presentation_session_messages_observer.h

+// 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.
+
+#ifndef CHROME_BROWSER_MEDIA_ROUTER_PRESENTATION_SESSION_MESSAGES_OBSERVER_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_PRESENTATION_SESSION_MESSAGES_OBSERVER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_vector.h"
+#include "chrome/browser/media/router/media_route.h"
+#include "content/public/browser/presentation_service_delegate.h"
+#include "content/public/browser/presentation_session.h"
+
+namespace media_router {
+
+class MediaRouter;
+
+// Observes messages originating from the MediaSink connected to a MediaRoute

[mark a. foltz, 2015/08/04 23:47:02]

Could this class be used for the 1-UA case?  In this case it would handle all
messages going *to* a PresentationSession, not just from a sink.

[imcheng, 2015/08/05 21:38:35]

That depends if 1-UA messaging will bypass the media router.

+// that represents a presentation.
+// Messages are received from MediaRouter via |OnMessagesReceived|, where
+// |message_cb_| will be invoked.
+class PresentationSessionMessagesObserver {
+ public:
+  // |message_cb|: The callback to invoke whenever messages are received.
+  // |route_id|: ID of MediaRoute to listen for messages.
+  PresentationSessionMessagesObserver(
+      const content::PresentationSessionMessageCallback& message_cb,
+      const MediaRoute::Id& route_id,
+      MediaRouter* router);
+  ~PresentationSessionMessagesObserver();
+
+  // Invoked by |router_| whenever messages are received. Invokes |message_cb_|
+  // with |messages|.
+  // |messages| is guaranteed to be non-empty.
+  void OnMessagesReceived(
+      const ScopedVector<content::PresentationSessionMessage>& messages);
+
+  const MediaRoute::Id& route_id() const { return route_id_; }
+
+ private:
+  content::PresentationSessionMessageCallback message_cb_;
+  const MediaRoute::Id route_id_;
+  MediaRouter* const router_;
+
+  DISALLOW_COPY_AND_ASSIGN(PresentationSessionMessagesObserver);
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_PRESENTATION_SESSION_MESSAGES_OBSERVER_H_