Allow JSObject::PreventExtensions to work for arguments objects.

src/objects.cc

 // Copyright 2011 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 3363 matching lines @@
   }
 
   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()) {
-    MaybeObject* result = NormalizeElements();
-    if (result->IsFailure()) return result;
+  NumberDictionary* dictionary = NULL;
+  { MaybeObject* maybe = NormalizeElements();
+    if (!maybe->To<NumberDictionary>(&dictionary)) return maybe;
   }
-  // TODO(kmillikin): Handle arguments object with dictionary elements.
-  ASSERT(HasDictionaryElements());
+  ASSERT(HasDictionaryElements() || HasDictionaryArgumentsElements());
   // Make sure that we never go back to fast case.
-  element_dictionary()->set_requires_slow_elements();
+  dictionary->set_requires_slow_elements();
 
   // Do a map transition, other objects with this map may still
   // be extensible.
-  Object* new_map;
-  { MaybeObject* maybe_new_map = map()->CopyDropTransitions();
-    if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
+  Map* new_map;
+  { MaybeObject* maybe = map()->CopyDropTransitions();
+    if (!maybe->To<Map>(&new_map)) return maybe;
   }
-  Map::cast(new_map)->set_is_extensible(false);
-  set_map(Map::cast(new_map));
+  new_map->set_is_extensible(false);
+  set_map(new_map);
   ASSERT(!map()->is_extensible());
   return new_map;
 }
 
 
 // Tests for the fast common case for property enumeration:
 // - This object and all prototypes has an enum cache (which means that it has
 //   no interceptors and needs no access checks).
 // - This object has no elements.
 // - No prototype has enumerable properties/elements.
@@ skipping 8281 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