Fix spec-compliance bug in Array.prototype.join.

test/mjsunit/array-join.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 73 matching lines @@
 assertEquals("", a.join(""));
 a[123123123] = "o";
 a[1255215215] = "p";
 assertEquals("op", a.join(""));
 
 a = new Array(100001);
 for (var i = 0; i < a.length; i++) a[i] = undefined;
 a[5] = "ab";
 a[90000] = "cd";
 assertEquals("abcd", a.join(""));  // Must not throw.
+
+
+// Make sure that each element is accessed exactly once, and in the correct
+// order.
+{
+  var log = [];
+  var p = new Proxy({length: 3, 0: 'a', 1: 'b'}, {
+      get: function(t, k, r) { log.push(k); return Reflect.get(t, k, r); }
+  });
+
+  assertEquals("a,b,", Array.prototype.join.call(p));
+  assertEquals(["length", "0", "1", "2"], log);
+}