the idea is that often times in code, you will see something like this:...

src/heap.h

 // Copyright 2006-2008 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 536 matching lines @@
   // Allocates a new SharedFunctionInfo object.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
   static Object* AllocateSharedFunctionInfo(Object* name);
 
   // Allocates a new cons string object.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
-  static Object* AllocateConsString(String* first, String* second);
+  static Object* AllocateConsString(String* first,
+                                    String* second,
+                                    PretenureFlag pretenure = NOT_TENURED);
 
   // Allocates a new sliced string object which is a slice of an underlying
   // string buffer stretching from the index start (inclusive) to the index
   // end (exclusive).
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
   static Object* AllocateSlicedString(String* buffer,
                                       int start,
                                       int end);
@@ skipping 1023 matching lines @@
   }
   static TranscendentalCache* caches_[kNumberOfCaches];
   Element elements_[kCacheSize];
   Type type_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_