Stop using plain Arrays internally in built-in functions.

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 5534 matching lines @@
         Top::context()->global_context()->initial_object_prototype();
   } else {
     map()->set_non_instance_prototype(false);
   }
 
   return SetInstancePrototype(construct_prototype);
 }
 
 
 Object* JSFunction::RemovePrototype() {
+  if (map() == context()->global_context()->function_without_prototype_map()) {
+    // Be idempotent.
+    return this;
+  }
   ASSERT(map() == context()->global_context()->function_map());
   set_map(context()->global_context()->function_without_prototype_map());
   set_prototype_or_initial_map(Heap::the_hole_value());
   return this;
 }
 
 
 Object* JSFunction::SetInstanceClassName(String* name) {
   shared()->set_instance_class_name(name);
   return this;
@@ skipping 4463 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