Add media router common classes and unittests.

chrome/browser/media/router/media_source_unittest.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_source.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace media_router {
+
+// Test that the object's getters match the constructor parameters.
+TEST(MediaSourceTest, Constructor) {
+  MediaSource source1("urn:x-com.google.cast:application:DEADBEEF");
+  EXPECT_EQ("urn:x-com.google.cast:application:DEADBEEF", source1.id());
+}
+
+}  // namespace media_router