Sanitize inheritance in callers of utils.expose

chrome/renderer/resources/extensions/automation/automation_event.js

Index: chrome/renderer/resources/extensions/automation/automation_event.js
diff --git a/chrome/renderer/resources/extensions/automation/automation_event.js b/chrome/renderer/resources/extensions/automation/automation_event.js
index 0ba408d9e82dae617c369e73ecc1d03c91487c35..70daef272b1faeaf00eeee6039545c164b7ae816 100644
--- a/chrome/renderer/resources/extensions/automation/automation_event.js
+++ b/chrome/renderer/resources/extensions/automation/automation_event.js
@@ -4,19 +4,21 @@
 
 var utils = require('utils');
 
-var AutomationEventImpl = function(type, target) {
+function AutomationEventImpl(type, target) {
   this.propagationStopped = false;
 
   // TODO(aboxhall): make these read-only properties
   this.type = type;
   this.target = target;
   this.eventPhase = Event.NONE;
-};
+}
+$Object.setPrototypeOf(AutomationEventImpl, null);
 
 AutomationEventImpl.prototype = {
+  __proto__: null,
   stopPropagation: function() {
     this.propagationStopped = true;
-  }
+  },
 };
 
 function AutomationEvent() {