Compile chrome://settings, part 9: yet another final battle

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.
  */
 
 /**
  * Verify |condition| is truthy and return |condition| if so.
@@ skipping 36 matching lines @@
  *
  * @param {string=} opt_message A message to show when this is hit.
  */
 function assertNotReached(opt_message) {
   throw new Error(opt_message || 'Unreachable code hit');
 }
 
 /**
  * @param {*} value The value to check.
  * @param {function(new: T, ...)} type A user-defined constructor.
+ * @param {string=} opt_message A message to show when this is hit.
  * @return {T}
  * @template T
  */
-function assertInstanceof(value, type) {
-  if (!(value instanceof type))
-    throw new Error(value + ' is not a[n] ' + (type.name || typeof type));
+function assertInstanceof(value, type, opt_message) {
+  if (!(value instanceof type)) {
+    throw new Error(opt_message ||
+                    value + ' is not a[n] ' + (type.name || typeof type));
+  }
   return value;
 }