Fix broken parent->child link in automation webView.

chrome/renderer/resources/extensions/automation_custom_bindings.js

Index: chrome/renderer/resources/extensions/automation_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/automation_custom_bindings.js b/chrome/renderer/resources/extensions/automation_custom_bindings.js
index 82a1e6c8bf5fe0bde75916f1414605dc178eed49..8b6cc2a5adeed285423e1f7eed03b6f6c90f8868 100644
--- a/chrome/renderer/resources/extensions/automation_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/automation_custom_bindings.js
@@ -211,7 +211,7 @@ automationInternal.onChildTreeID.addListener(function(treeID,
   if (!subroot) {
     automationUtil.storeTreeCallback(childTreeID, function(root) {
       privates(root).impl.setHostNode(node);
-
+      privates(node).impl.childTree = root;
       if (root.docLoaded)
         privates(root).impl.dispatchEvent(schema.EventType.loadComplete);
 
@@ -221,6 +221,7 @@ automationInternal.onChildTreeID.addListener(function(treeID,
     automationInternal.enableFrame(childTreeID);
   } else {
     privates(subroot).impl.setHostNode(node);
+    privates(node).impl.childTree = subroot;
   }
 });