Typecheck some of ui/webui/resources/js/ with Closure compiler.

ui/webui/resources/js/assert.js

 // Copyright (c) 2013 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.
 
 /**
  * @fileoverview Assertion support.
  */
 
 /**
  * Simple common assertion API
  * @param {*} condition The condition to test.  Note that this may be used to
  *     test whether a value is defined or not, and we don't want to force a
  *     cast to Boolean.
  * @param {string=} opt_message A message to use in any error.
  */
 function assert(condition, opt_message) {
   'use strict';
   if (!condition) {
     var msg = 'Assertion failed';
     if (opt_message)
       msg = msg + ': ' + opt_message;
     throw new Error(msg);
   }
 }
+
+/**
+ * Insert a notReached() in cases where control flow should never hit.
+ * @param {string=} opt_message A message to show when this is hit.
+ */
+function notReached(opt_message) {

[arv (Not doing code reviews), 2014/07/24 16:44:24]

How about assertNotReached instead?

[Dan Beam, 2014/07/25 01:52:32]

hmmm, blink uses ASSERT_NOT_REACHED() while chrome uses NOTREACHED.

"assertNotReached" is clearer than "notReached" (arguably), but
"assertNotReached" is longer than "assert(false, " or "notReached".

whatever, "assertNotReached" it is.

+  throw new Error(opt_message || "Unreachable code hit");
+}