Avoid convertion to double when it is not needed.

src/factory.h

 // 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 248 matching lines @@
       Handle<FixedDoubleArray> array);
 
   // Numbers (e.g. literals) are pretenured by the parser.
   Handle<Object> NewNumber(double value,
                            PretenureFlag pretenure = NOT_TENURED);
 
   Handle<Object> NewNumberFromInt(int32_t value,
                                   PretenureFlag pretenure = NOT_TENURED);
   Handle<Object> NewNumberFromUint(uint32_t value,
                                   PretenureFlag pretenure = NOT_TENURED);
-
+  inline Handle<Object> NewNumberFromSize(size_t value,
+                                   PretenureFlag pretenure = NOT_TENURED);
   Handle<HeapNumber> NewHeapNumber(double value,
                                    PretenureFlag pretenure = NOT_TENURED);
 
+
   // These objects are used by the api to create env-independent data
   // structures in the heap.
   Handle<JSObject> NewNeanderObject();
 
   Handle<JSObject> NewArgumentsObject(Handle<Object> callee, int length);
 
   // JS objects are pretenured when allocated by the bootstrapper and
   // runtime.
   Handle<JSObject> NewJSObject(Handle<JSFunction> constructor,
                                PretenureFlag pretenure = NOT_TENURED);
@@ skipping 249 matching lines @@
   // Create a new map cache.
   Handle<MapCache> NewMapCache(int at_least_space_for);
 
   // Update the map cache in the native context with (keys, map)
   Handle<MapCache> AddToMapCache(Handle<Context> context,
                                  Handle<FixedArray> keys,
                                  Handle<Map> map);
 };
 
 
+Handle<Object> Factory::NewNumberFromSize(size_t value,
+                                          PretenureFlag pretenure) {
+  if (Smi::IsValid(static_cast<intptr_t>(value))) {
+    return Handle<Object>(Smi::FromIntptr(static_cast<intptr_t>(value)),
+                          isolate());
+  } else {
+    return NewNumber(static_cast<double>(value), pretenure);
+  }
+}
+
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_