Use mutable heapnumbers to store doubles in fields.

src/string-stream.cc

 // Copyright 2012 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 350 matching lines @@
           len = String::cast(key)->length();
         }
         for (; len < 18; len++)
           Put(' ');
         if (key->IsString()) {
           Put(String::cast(key));
         } else {
           key->ShortPrint();
         }
         Add(": ");
-        Object* value = js_object->FastPropertyAt(descs->GetFieldIndex(i));
+        Object* value = js_object->RawFastPropertyAt(descs->GetFieldIndex(i));
         Add("%o\n", value);
       }
     }
   }
 }
 
 
 void StringStream::PrintFixedArray(FixedArray* array, unsigned int limit) {
   Heap* heap = HEAP;
   for (unsigned int i = 0; i < 10 && i < limit; i++) {
@@ skipping 203 matching lines @@
 
 // Only grow once to the maximum allowable size.
 char* NoAllocationStringAllocator::grow(unsigned* bytes) {
   ASSERT(size_ >= *bytes);
   *bytes = size_;
   return space_;
 }
 
 
 } }  // namespace v8::internal