[Extensions] Don't allow built-in extensions code to be overridden

extensions/renderer/resources/uncaught_exception_handler.js

 // 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.
 
 // Handles uncaught exceptions thrown by extensions. By default this is to
 // log an error message, but tests may override this behaviour.
 var handler = function(message, e) {
   console.error(message);
 };
 
@@ skipping 77 matching lines @@
 }
 
 /**
  * Formats the error message and invokes the error handler.
  *
  * @param {string} message - Error message prefix.
  * @param {Error|*} e - Thrown object.
  * @param {string=} priorStackTrace - Error message suffix.
  * @see formatErrorMessage
  */
-exports.handle = function(message, e, priorStackTrace) {
+exports.$set('handle', function(message, e, priorStackTrace) {
   message = formatErrorMessage(message, e, priorStackTrace);
   handler(message, e);
-};
+});
 
 // |newHandler| A function which matches |handler|.
-exports.setHandler = function(newHandler) {
+exports.$set('setHandler', function(newHandler) {
   handler = newHandler;
-};
+});
 
-exports.getStackTrace = getStackTrace;
-exports.getExtensionStackTrace = getExtensionStackTrace;
-exports.safeErrorToString = safeErrorToString;
+exports.$set('getStackTrace', getStackTrace);
+exports.$set('getExtensionStackTrace', getExtensionStackTrace);
+exports.$set('safeErrorToString', safeErrorToString);