Make the RegExp.prototype object be a RegExp object.

src/bootstrapper.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 977 matching lines @@
     descriptors->SetNextEnumerationIndex(enum_index);
     descriptors->Sort();
 
     initial_map->set_inobject_properties(5);
     initial_map->set_pre_allocated_property_fields(5);
     initial_map->set_unused_property_fields(0);
     initial_map->set_instance_size(
         initial_map->instance_size() + 5 * kPointerSize);
     initial_map->set_instance_descriptors(*descriptors);
     initial_map->set_visitor_id(StaticVisitorBase::GetVisitorId(*initial_map));
+
+    // RegExp prototype object is itself a RegExp.
+    Handle<Map> proto_map = factory->CopyMapDropTransitions(initial_map);
+    proto_map->set_prototype(global_context()->initial_object_prototype());
+    Handle<JSObject> proto = factory->NewJSObjectFromMap(proto_map);
+    proto->InObjectPropertyAtPut(JSRegExp::kSourceFieldIndex,
+                                 heap->empty_string());
+    proto->InObjectPropertyAtPut(JSRegExp::kGlobalFieldIndex,
+                                 heap->false_value());
+    proto->InObjectPropertyAtPut(JSRegExp::kIgnoreCaseFieldIndex,
+                                 heap->false_value());
+    proto->InObjectPropertyAtPut(JSRegExp::kMultilineFieldIndex,
+                                 heap->false_value());
+    proto->InObjectPropertyAtPut(JSRegExp::kLastIndexFieldIndex,
+                                 Smi::FromInt(0),
+                                 SKIP_WRITE_BARRIER);  // It's a Smi.
+    initial_map->set_prototype(*proto);
+    factory->SetRegExpIrregexpData(Handle<JSRegExp>::cast(proto),
+                                   JSRegExp::IRREGEXP, factory->empty_string(),
+                                   JSRegExp::Flags(0), 0);
   }
 
   {  // -- J S O N
     Handle<String> name = factory->NewStringFromAscii(CStrVector("JSON"));
     Handle<JSFunction> cons = factory->NewFunction(
         name,
         factory->the_hole_value());
     cons->SetInstancePrototype(global_context()->initial_object_prototype());
     cons->SetInstanceClassName(*name);
     Handle<JSObject> json_object = factory->NewJSObject(cons, TENURED);
@@ skipping 1237 matching lines @@
   return from + sizeof(NestingCounterType);
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   ASSERT(!IsActive());
 }
 
 } }  // namespace v8::internal