[builtins] Get rid of a few %_ClassOf uses.

src/js/harmony-atomics.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();
 
@@ skipping 14 matching lines @@
 
 
 function CheckSharedIntegerTypedArray(ia) {
   if (!%IsSharedIntegerTypedArray(ia)) {
     throw MakeTypeError(kNotIntegerSharedTypedArray, ia);
   }
 }
 
 function CheckSharedInteger32TypedArray(ia) {
   CheckSharedIntegerTypedArray(ia);
-  if (%_ClassOf(ia) !== 'Int32Array') {
+  if (!%IsSharedInteger32TypedArray(ia)) {
     throw MakeTypeError(kNotInt32SharedTypedArray, ia);
   }
 }
 
 //-------------------------------------------------------------------
 
 function AtomicsCompareExchangeJS(sta, index, oldValue, newValue) {
   CheckSharedIntegerTypedArray(sta);
   index = TO_INTEGER(index);
   if (index < 0 || index >= %_TypedArrayGetLength(sta)) {
@@ skipping 160 matching lines @@
   "or", AtomicsOrJS,
   "xor", AtomicsXorJS,
   "exchange", AtomicsExchangeJS,
   "isLockFree", AtomicsIsLockFreeJS,
   "futexWait", AtomicsFutexWaitJS,
   "futexWake", AtomicsFutexWakeJS,
   "futexWakeOrRequeue", AtomicsFutexWakeOrRequeueJS,
 ]);
 
 })