[MediaRouter UI] Compile MR WebUI js code with Closure.

chrome/browser/resources/media_router/externs.js

 // 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 "ipc/ipc_handle_win.h"
+/**
+ * @fileoverview Externs to be declared to properly compile JS code.
+ * @externs
+ */
 
-namespace IPC {
+var performance = {};
 
-HandleForTransit CreateHandleForTransit(HANDLE handle) {
-  HandleForTransit hft;
-  hft.handle = handle;
-  return hft;
-}
-
-}  // namespace IPC
+/**
+ * @return {number}
+ */
+performance.now = function() {};