Add a separate scope for switch

test/mjsunit/regress/regress-4377.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.
+
+// See: http://code.google.com/p/v8/issues/detail?id=4377
+
+// Switch statements should introduce their own lexical scope
+
+'use strict';
+
+switch (1) { case 1: let x = 2; }
+
+assertThrows(() => x, ReferenceError);
+
+{
+  let result;
+  let x = 1;
+  switch (x) {
+    case 1:
+      let x = 2;
+      result = x;
+      break;
+    default:
+      result = 0;
+      break;
+  }
+  assertEquals(1, x);
+  assertEquals(2, result);
+}
+
+{
+  let result;
+  let x = 1;
+  switch (eval('x')) {
+    case 1:
+      let x = 2;
+      result = x;
+      break;
+    default:
+      result = 0;
+      break;
+  }
+  assertEquals(1, x);
+  assertEquals(2, result);
+}