Update json_schema_compiler to handle the Automation extension API

chrome/browser/resources/chromeos/chromevox/cvox2/background/custom_automation_event.js

+// Copyright 2017 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 Custom Automation Event.
+ *
+ * An object similar to a chrome.automation.AutomationEvent that we can
+ * construct, unlike the object from the extension system.
+ */
+
+goog.provide('CustomAutomationEvent');
+
+/**
+ * An object we can use instead of a chrome.automation.AutomationEvent.
+ * @constructor
+ * @extends {chrome.automation.AutomationEvent}
+ * @param {chrome.automation.EventType} type The event type.
+ * @param {!chrome.automation.AutomationNode} target The event target.
+ * @param {string} eventFrom The source of this event.
+ */
+var CustomAutomationEvent = function(type, target, eventFrom) {
+  this.type = type;
+  this.target = target;
+  this.eventFrom = eventFrom;
+};
+
+/**
+ * @override
+ */
+CustomAutomationEvent.prototype.stopPropagation = function() {
+  throw Error('Can\'t call stopPropagation on a CustomAutomationEvent');
+};