Handle variable set in inferrer

tests/compiler/dart2js/inference/data/locals.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /*element: main:[null]*/
 main() {
   uninitializedLocal();
   initializedLocal();
+  updatedLocal();
 }
 
 /*element: uninitializedLocal:[null]*/
 uninitializedLocal() {
   var local;
   return local;
 }
 
 /*element: initializedLocal:[exact=JSUInt31]*/
 initializedLocal() {
   var local = 0;
   return local;
 }
+
+/*element: updatedLocal:[exact=JSUInt31]*/
+updatedLocal() {
+  var local2;
+  local2 = 0;
+  return local2;
+}