Add a lexical scope for the body of a with statement

test/mjsunit/regress/regress-542100.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: --harmony-sloppy --harmony-sloppy-function
+
+(function() {
+  var x = {a: 1}
+  assertEquals("undefined", typeof f);
+  with (x)
+    function f() { return a; }
+  assertEquals("function", typeof f);
+  assertEquals(1, f());
+  x.a = 2;
+  assertEquals(2, f());
+})();
+
+var y = {b: 1}
+assertEquals("undefined", typeof g);
+with (y)
+  function g() { return b; }
+assertEquals("function", typeof g);
+assertEquals(1, g());
+y.b = 2;
+assertEquals(2, g());