Use mutable heapnumbers to store doubles in fields.

src/objects-printer.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 253 matching lines @@
 void JSObject::PrintProperties(FILE* out) {
   if (HasFastProperties()) {
     DescriptorArray* descs = map()->instance_descriptors();
     for (int i = 0; i < map()->NumberOfOwnDescriptors(); i++) {
       PrintF(out, "   ");
       descs->GetKey(i)->NamePrint(out);
       PrintF(out, ": ");
       switch (descs->GetType(i)) {
         case FIELD: {
           int index = descs->GetFieldIndex(i);
-          FastPropertyAt(index)->ShortPrint(out);
+          RawFastPropertyAt(index)->ShortPrint(out);
           PrintF(out, " (field at offset %d)\n", index);
           break;
         }
         case CONSTANT_FUNCTION:
           descs->GetConstantFunction(i)->ShortPrint(out);
           PrintF(out, " (constant function)\n");
           break;
         case CALLBACKS:
           descs->GetCallbacksObject(i)->ShortPrint(out);
           PrintF(out, " (callback)\n");
@@ skipping 922 matching lines @@
     }
   }
   PrintF(out, "\n");
 }
 
 
 #endif  // OBJECT_PRINT
 
 
 } }  // namespace v8::internal