Native context: do not put public symbols and flags on the js builtins object.

src/harmony-sharedarraybuffer.js

 // Copyright 2015 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.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
 var GlobalSharedArrayBuffer = global.SharedArrayBuffer;
 var GlobalObject = global.Object;
+var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
 
 // -------------------------------------------------------------------
 
 function SharedArrayBufferConstructor(length) { // length = 1
   if (%_IsConstructCall()) {
     var byteLength = $toPositiveInteger(length, kInvalidArrayBufferLength);
     %ArrayBufferInitialize(this, byteLength, kShared);
   } else {
     throw MakeTypeError(kConstructorNotFunction, "SharedArrayBuffer");
   }
@@ skipping 14 matching lines @@
 
 // Set up the SharedArrayBuffer constructor function.
 %SetCode(GlobalSharedArrayBuffer, SharedArrayBufferConstructor);
 %FunctionSetPrototype(GlobalSharedArrayBuffer, new GlobalObject());
 
 // Set up the constructor property on the SharedArrayBuffer prototype object.
 %AddNamedProperty(GlobalSharedArrayBuffer.prototype, "constructor",
                   GlobalSharedArrayBuffer, DONT_ENUM);
 
 %AddNamedProperty(GlobalSharedArrayBuffer.prototype,
-    symbolToStringTag, "SharedArrayBuffer", DONT_ENUM | READ_ONLY);
+    toStringTagSymbol, "SharedArrayBuffer", DONT_ENUM | READ_ONLY);
 
 utils.InstallGetter(GlobalSharedArrayBuffer.prototype, "byteLength",
                     SharedArrayBufferGetByteLen);
 
 utils.InstallFunctions(GlobalSharedArrayBuffer, DONT_ENUM, [
     "isView", SharedArrayBufferIsViewJS
 ]);
 
 })