[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 {
+
+SinksQueryResult::SinksQueryResult() {
+}
+
+SinksQueryResult::~SinksQueryResult() {
+}
+
+MediaSinksObserver::MediaSinksObserver(const MediaSource& source)
+    : source_(source),
+      registered_(false) {
+}
+
+MediaSinksObserver::~MediaSinksObserver() {
+  DCHECK(!registered_);
+}
+
+}  // namespace media_router