Factor out core of Array.forEach and .every, for use in TypedArrays

test/mjsunit/harmony/typedarrays-every.js

 // Copyright 2014 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.
 
 // Flags: --harmony-arrays --allow-natives-syntax
 
 var typedArrayConstructors = [
   Uint8Array,
   Int8Array,
   Uint16Array,
@@ skipping 67 matching lines @@
   CheckWrapping(false, Boolean);
   CheckWrapping("xxx", String);
   CheckWrapping(42, Number);
   CheckWrapping(3.14, Number);
   CheckWrapping({}, Object);
 
   // Neutering the buffer backing the typed array mid-way should
   // still make .forEach() finish, and the array should keep being
   // empty after neutering it.
   count = 0;
-  a = new constructor(2);
+  a = new constructor(3);
   result = a.every(function (n, index, array) {
+    assertFalse(array[index] === undefined);  // don't get here if neutered
     if (count > 0) %ArrayBufferNeuter(array.buffer);
     array[index] = n + 1;
     count++;
     return count > 1 ? array[index] === undefined : true;
   });
   assertEquals(2, count);
   assertEquals(true, result);
   CheckTypedArrayIsNeutered(a);
   assertEquals(undefined, a[0]);
 
@@ skipping 32 matching lines @@
     count = 0;
     a = new typedArrayConstructors[i](4);
     constructor.prototype.every.call(a, function (x) { count++; return true; });
     assertEquals(a.length, count);
   }
 }
 
 for (i = 0; i < typedArrayConstructors.length; i++) {
   TestTypedArrayForEach(typedArrayConstructors[i]);
 }