[strong] Deprecate for-in

test/mjsunit/strong/for-in.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.
+
+// Flags: --strong-mode
+
+(function NoForInStatement() {
+  assertThrows("'use strong'; for (x in []) {}", SyntaxError);
+  assertThrows("'use strong'; for (let x in []) {}", SyntaxError);
+  assertThrows("'use strong'; for (const x in []) {}", SyntaxError);
+})();
+
+(function ForOfStatement() {
+  assertTrue(eval("'use strong'; for (x of []) {} true"));
+  assertTrue(eval("'use strong'; for (let x of []) {} true"));
+  assertTrue(eval("'use strong'; for (const x of []) {} true"));
+})();