Make ChromeVox navigation 100x faster on some sites.

chrome/renderer/resources/extensions/automation/automation_node.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.
 
 var AutomationEvent = require('automationEvent').AutomationEvent;
 var automationInternal =
     require('binding').Binding.create('automationInternal').generate();
 var exceptionHandler = require('uncaught_exception_handler');
 var IsInteractPermitted =
     requireNative('automationInternal').IsInteractPermitted;
@@ skipping 289 matching lines @@
     for (var i = 0; i < count; ++i) {
       var childID = GetChildIDAtIndex(this.treeID, this.id, i);
       var child = this.rootImpl.get(childID);
       $Array.push(children, child);
     }
     return children;
   },
 
   get previousSibling() {
     var parent = this.parent;
+    if (!parent)
+      return undefined;
+    parent = privates(parent).impl;
     var indexInParent = GetIndexInParent(this.treeID, this.id);
-    if (parent && indexInParent > 0)
-      return parent.children[indexInParent - 1];
-    return undefined;
+    return this.rootImpl.get(
+        GetChildIDAtIndex(parent.treeID, parent.id, indexInParent - 1));
   },
 
   get nextSibling() {
     var parent = this.parent;
+    if (!parent)
+      return undefined;
+    parent = privates(parent).impl;
     var indexInParent = GetIndexInParent(this.treeID, this.id);
-    if (parent && indexInParent < parent.children.length)
-      return parent.children[indexInParent + 1];
-    return undefined;
+    return this.rootImpl.get(
+        GetChildIDAtIndex(parent.treeID, parent.id, indexInParent + 1));
   },
 
   doDefault: function() {
     this.performAction_('doDefault');
   },
 
   focus: function() {
     this.performAction_('focus');
   },
 
@@ skipping 718 matching lines @@
 utils.defineProperty(AutomationRootNode, 'getOrCreate', function(treeID) {
   return AutomationRootNodeImpl.getOrCreate(treeID);
 });
 
 utils.defineProperty(AutomationRootNode, 'destroy', function(treeID) {
   AutomationRootNodeImpl.destroy(treeID);
 });
 
 exports.$set('AutomationNode', AutomationNode);
 exports.$set('AutomationRootNode', AutomationRootNode);