Add access checks to Object.preventExtensions + add regression test for 1027....

src/runtime.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 3655 matching lines @@
   uint32_t index;
   bool is_element = name->AsArrayIndex(&index);
 
   // Special case for elements if any of the flags are true.
   // If elements are in fast case we always implicitly assume that:
   // DONT_DELETE: false, DONT_ENUM: false, READ_ONLY: false.
   if (((unchecked & (DONT_DELETE | DONT_ENUM | READ_ONLY)) != 0) &&
       is_element) {
     // Normalize the elements to enable attributes on the property.
     if (js_object->IsJSGlobalProxy()) {
+      // We do not need to do access checks here since these has already
+      // been performed by the call to GetOwnProperty.
       Handle<Object> proto(js_object->GetPrototype());
       // If proxy is detached, ignore the assignment. Alternatively,
       // we could throw an exception.
       if (proto->IsNull()) return *obj_value;
       js_object = Handle<JSObject>::cast(proto);
     }
     NormalizeElements(js_object);
     Handle<NumberDictionary> dictionary(js_object->element_dictionary());
     // Make sure that we never go back to fast case.
     dictionary->set_requires_slow_elements();
@@ skipping 7515 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal