Add media router common classes and unittests.

chrome/browser/media/router/media_sink.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_sink.h"
+
+namespace media_router {
+
+MediaSink::MediaSink(const MediaSinkId& sink_id,
+                     const std::string& name)
+    : sink_id_(sink_id), name_(name) {
+}
+
+MediaSink::~MediaSink() {
+}
+
+bool MediaSink::Equals(const MediaSink& other) const {
+  return sink_id_ == other.sink_id_;
+}
+
+}  // namespace media_router