Fix issue with Array.concat not preserving holes in the

test/mjsunit/array-concat.js

 // Copyright 2008 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 89 matching lines @@
   assertEquals("undefined", typeof(c[0xffffffff]));
   assertEquals(c.length, a.length + 1);
 
 }
 
 a = [];
 c = a.concat('Hello');
 assertEquals(1, c.length);
 assertEquals("Hello", c[0]);
 assertEquals("Hello", c.toString());
+
+// Check that concat preserves holes.
+var holey = [void 0,'a',,'c'].concat(['d',,'f',[0,,2],void 0])
+assertEquals(9, holey.length);  // hole in embedded array is ignored
+for (var i = 0; i < holey.length; i++) {
+  if (i == 2 || i == 5) {
+    assertFalse(i in holey);
+  } else {
+    assertTrue(i in holey);
+  }
+}