Add media router common classes and unittests.

chrome/browser/media/router/media_source.cc

Index: chrome/browser/media/router/media_source.cc
diff --git a/chrome/browser/media/router/media_source.cc b/chrome/browser/media/router/media_source.cc
new file mode 100644
index 0000000000000000000000000000000000000000..88fc2849cdef5e07b3c726bdef31a5d50ed573dc
--- /dev/null
+++ b/chrome/browser/media/router/media_source.cc
@@ -0,0 +1,21 @@
+// 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_source.h"
+
+#include <string>
+
+namespace media_router {
+
+MediaSource::MediaSource(const std::string& source_id)
+    : id_(source_id) {
+}
+
+MediaSource::~MediaSource() {}
+
+std::string MediaSource::id() const {
+  return id_;
+}
+
+}  // namespace media_router