[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_routes_observer.cc

Index: chrome/browser/media/router/media_routes_observer.cc
diff --git a/chrome/browser/media/router/media_routes_observer.cc b/chrome/browser/media/router/media_routes_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..58f76d340791b8ba35dcbb45bededc2e015ec31b
--- /dev/null
+++ b/chrome/browser/media/router/media_routes_observer.cc
@@ -0,0 +1,17 @@
+// 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_routes_observer.h"
+
+#include "base/logging.h"
+
+namespace media_router {
+
+MediaRoutesObserver::MediaRoutesObserver() : registered_(false) {}
+
+MediaRoutesObserver::~MediaRoutesObserver() {
+  DCHECK(!registered_);
+}
+
+}  // namespace media_router