Make sure that we never call prevent extension on the global proxy,...

src/objects.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2761 matching lines @@
       return context->extension()->ReferencesObject(obj);
     }
   }
 
   // No references to object.
   return false;
 }
 
 
 MaybeObject* JSObject::PreventExtensions() {
+  if (IsJSGlobalProxy()) {
+    Object* proto = GetPrototype();
+    if (proto->IsNull()) return this;
+    ASSERT(proto->IsJSGlobalObject());
+    return JSObject::cast(proto)->PreventExtensions();
+  }
+
   // If there are fast elements we normalize.
   if (HasFastElements()) {
     Object* ok;
     { MaybeObject* maybe_ok = NormalizeElements();
       if (!maybe_ok->ToObject(&ok)) return maybe_ok;
     }
   }
   // Make sure that we never go back to fast case.
   element_dictionary()->set_requires_slow_elements();
 
@@ skipping 7108 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 
 } }  // namespace v8::internal