Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/handles.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 664 matching lines @@
       if (!(details.IsDontEnum() || key->IsSymbol())) {
         storage->set(index, key);
         if (!indices.is_null()) {
           if (details.type() != FIELD) {
             indices = Handle<FixedArray>();
           } else {
             int field_index = descs->GetFieldIndex(i);
             if (field_index >= map->inobject_properties()) {
               field_index = -(field_index - map->inobject_properties() + 1);
             }
+            field_index = (field_index << 1)
+                | details.representation().IsDouble();
             indices->set(index, Smi::FromInt(field_index));
           }
         }
         index++;
       }
     }
     ASSERT(index == storage->length());
 
     Handle<FixedArray> bridge_storage =
         isolate->factory()->NewFixedArray(
@@ skipping 64 matching lines @@
                                    Handle<Code> code) {
   heap->EnsureWeakObjectToCodeTable();
   Handle<DependentCode> dep(heap->LookupWeakObjectToCodeDependency(*object));
   dep = DependentCode::Insert(dep, DependentCode::kWeaklyEmbeddedGroup, code);
   CALL_HEAP_FUNCTION_VOID(heap->isolate(),
                           heap->AddWeakObjectToCodeDependency(*object, *dep));
 }
 
 
 } }  // namespace v8::internal