[es6] Ensure that for-in/of loops have a proper TDZ for their boundnames

test/mjsunit/es6/regress/regress-2506.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.
 
 'use strict';
 
 // Top-level code
 let s = 0;
 let f = [undefined, undefined, undefined]
 for (const x of [1,2,3]) {
   s += x;
   f[x-1] = function() { return x; }
 }
 assertEquals(6, s);
 assertEquals(1, f[0]());
 assertEquals(2, f[1]());
 assertEquals(3, f[2]());
 
 let x = 1;
 s = 0;
-for (const x of [x, x+1, x+2]) {
-  s += x;
+for (const z of [x, x+1, x+2]) {
+  s += z;
 }
 assertEquals(6, s);
 
 s = 0;
 var q = 1;
-for (const q of [q, q+1, q+2]) {
-  s += q;
+for (const x of [q, q+1, q+2]) {
+  s += x;
 }
 assertEquals(6, s);
 
 let z = 1;
 s = 0;
 for (const x = 1; z < 2; z++) {
   s += x + z;
 }
 assertEquals(2, s);
 
 
 s = "";
 for (const x in [1,2,3]) {
   s += x;
 }
 assertEquals("012", s);
 
 assertThrows("'use strict'; for (const x in [1,2,3]) { x++ }", TypeError);
 
 // Function scope
 (function() {
   let s = 0;
   for (const x of [1,2,3]) {
     s += x;
   }
   assertEquals(6, s);
 
   let x = 1;
   s = 0;
-  for (const x of [x, x+1, x+2]) {
-    s += x;
+  for (const q of [x, x+1, x+2]) {
+    s += q;
   }
   assertEquals(6, s);
 
   s = 0;
   var q = 1;
-  for (const q of [q, q+1, q+2]) {
-    s += q;
+  for (const x of [q, q+1, q+2]) {
+    s += x;
   }
   assertEquals(6, s);
 
   s = "";
   for (const x in [1,2,3]) {
     s += x;
   }
   assertEquals("012", s);
 }());