Revert "Replace HeapNumber as doublebox with an explicit MutableHeapNumber."

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 14497 matching lines @@
   FieldIndex field_index =
       FieldIndex::ForLoadByFieldIndex(object->map(), index->value());
   if (field_index.is_inobject()) {
     RUNTIME_ASSERT(field_index.property_index() <
                    object->map()->inobject_properties());
   } else {
     RUNTIME_ASSERT(field_index.outobject_array_index() <
                    object->properties()->length());
   }
   Handle<Object> raw_value(object->RawFastPropertyAt(field_index), isolate);
-  RUNTIME_ASSERT(raw_value->IsMutableHeapNumber());
-  return *Object::WrapForRead(isolate, raw_value, Representation::Double());
+  RUNTIME_ASSERT(raw_value->IsNumber() || raw_value->IsUninitialized());
+  return *Object::NewStorageFor(isolate, raw_value, Representation::Double());
 }
 
 
 RUNTIME_FUNCTION(Runtime_TryMigrateInstance) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
   if (!object->IsJSObject()) return Smi::FromInt(0);
   Handle<JSObject> js_object = Handle<JSObject>::cast(object);
   if (!js_object->map()->is_deprecated()) return Smi::FromInt(0);
@@ skipping 560 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal