Avoid map transitions and multiple backing arrays for builtin prototypes...

src/spaces.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 1532 matching lines @@
   virtual Address PageAllocationTop(Page* page) {
     return page == TopPageOf(allocation_info_) ? top()
         : page->ObjectAreaEnd() - page_extra_;
   }
 
   int object_size_in_bytes() { return object_size_in_bytes_; }
 
   // Give a fixed sized block of memory to the space's free list.
   void Free(Address start) {
     free_list_.Free(start);
-    accounting_stats_.DeallocateBytes(Map::kSize);
+    accounting_stats_.DeallocateBytes(object_size_in_bytes_);
   }
 
   // Prepares for a mark-compact GC.
   virtual void PrepareForMarkCompact(bool will_compact);
 
   // Updates the allocation pointer to the relocation top after a mark-compact
   // collection.
   virtual void MCCommitRelocationInfo();
 
 #ifdef DEBUG
@@ skipping 248 matching lines @@
 
  private:
   LargeObjectChunk* current_;
   HeapObjectCallback size_func_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_