[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_sinks_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/media_sinks_observer.h"
+
+#include "base/logging.h"
 #include "chrome/browser/media/router/media_sink.h"
 
 namespace media_router {
 
-MediaSink::MediaSink(const MediaSinkId& sink_id,
-                     const std::string& name)
-    : sink_id_(sink_id), name_(name) {
+MediaSinksObserver::MediaSinksObserver(const MediaSource& source)
+    : source_(source),
+      registered_(false) {
 }
 
-MediaSink::~MediaSink() {
-}
-
-bool MediaSink::Equals(const MediaSink& other) const {
-  return sink_id_ == other.sink_id_;
+MediaSinksObserver::~MediaSinksObserver() {
+  DCHECK(!registered_);
 }
 
 }  // namespace media_router