[parser] Fix scopes in rewriting of for-of and destructuring assignments.

test/mjsunit/regress/regress-5648.js

+// Copyright 2016 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.
+
+
+var iter = {}
+iter[Symbol.iterator] = () => ({
+  next: () => ({}),
+  return: () => {throw 666}
+});
+
+
+function* foo() {
+  for (let x of iter) {throw 42}
+}
+assertThrowsEquals(() => foo().next(), 42);
+
+
+function* bar() {
+  let x;
+  { let gaga = () => {x};
+    [[x]] = iter;
+  }
+}
+assertThrows(() => bar().next(), TypeError);
+
+
+function baz() {
+  let x;
+  { let gaga = () => {x};
+    let gugu = () => {gaga};
+    [[x]] = iter;
+  }
+}
+assertThrows(baz, TypeError);