Add media router common classes and unittests.

chrome/browser/media/router/media_cast_mode.cc

+// Copyright 2014 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_cast_mode.h"
+
+#include "base/logging.h"
+
+namespace media_router {
+
+// TODO(haibinlu): use localized string.
+std::string MediaCastModeToTitle(MediaCastMode mode) {
+  switch (mode) {
+    case MediaCastMode::APP_CAST:
+      return "Cast [website here]";
+    case MediaCastMode::SCREEN_WINDOW_MIRROR:
+      return "Cast screen/window";
+    case MediaCastMode::SOUND_OPTIMIZED_TAB_MIRROR:
+      return "Cast this tab (optimize for audio)";
+    case MediaCastMode::TAB_MIRROR:
+      return "Cast this tab";
+    default:
+      NOTREACHED();
+      return "";
+  }
+}
+
+}  // namespace media_router