Do not export natives to runtime via js builtins object.

src/object-observe.js

 // Copyright 2012 the V8 project 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 $observeNotifyChange;
 var $observeEnqueueSpliceRecord;
 var $observeBeginPerformSplice;
 var $observeEndPerformSplice;
-var $observeNativeObjectObserve;
-var $observeNativeObjectGetNotifier;
-var $observeNativeObjectNotifierPerformChange;
 
 var $observeObjectMethods;
 var $observeArrayMethods;
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 674 matching lines @@
 ];
 
 // TODO(adamk): Figure out why this prototype removal has to
 // happen as part of initial snapshotting.
 var removePrototypeFn = function(f, i) {
   if (i % 2 === 1) %FunctionRemovePrototype(f);
 };
 $observeObjectMethods.forEach(removePrototypeFn);
 $observeArrayMethods.forEach(removePrototypeFn);
 
-$observeNotifyChange = NotifyChange;
 $observeEnqueueSpliceRecord = EnqueueSpliceRecord;
 $observeBeginPerformSplice = BeginPerformSplice;
 $observeEndPerformSplice = EndPerformSplice;
-$observeNativeObjectObserve = NativeObjectObserve;
-$observeNativeObjectGetNotifier = NativeObjectGetNotifier;
-$observeNativeObjectNotifierPerformChange = NativeObjectNotifierPerformChange;
+
+utils.ExportToRuntime(function(to) {
+  to.ObserveNotifyChange = NotifyChange;
+  to.ObserveEnqueueSpliceRecord = EnqueueSpliceRecord;
+  to.ObserveBeginPerformSplice = BeginPerformSplice;
+  to.ObserveEndPerformSplice = EndPerformSplice;
+  to.ObserveNativeObjectObserve = NativeObjectObserve;
+  to.ObserveNativeObjectGetNotifier = NativeObjectGetNotifier;
+  to.ObserveNativeObjectNotifierPerformChange =
+      NativeObjectNotifierPerformChange;
+});
 
 })