Do not export natives to runtime via js builtins object.

src/runtime.js

 // Copyright 2006-2008 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.
 
 // This files contains runtime support implemented in JavaScript.
 
 // CAUTION: Some of the functions specified in this file are called
 // directly from compiled code. These are the functions with names in
 // ALL CAPS. The compiled code passes the first argument in 'this'.
 
@@ skipping 897 matching lines @@
 
 //----------------------------------------------------------------------------
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype(GlobalArray, new GlobalArray(0));
 
-//----------------------------------------------------------------------------
+// ----------------------------------------------------------------------------
 
 $concatIterableToArray = ConcatIterableToArray;
 $defaultNumber = DefaultNumber;
 $defaultString = DefaultString;
 $NaN = %GetRootNaN();
 $nonNumberToNumber = NonNumberToNumber;
 $nonStringToString = NonStringToString;
 $sameValue = SameValue;
 $sameValueZero = SameValueZero;
 $toBoolean = ToBoolean;
 $toInteger = ToInteger;
 $toLength = ToLength;
 $toName = ToName;
 $toNumber = ToNumber;
 $toPositiveInteger = ToPositiveInteger;
 $toPrimitive = ToPrimitive;
 $toString = ToString;
 
 })