Make RegExp constructor non-const.

utils/tests/pub/update/hosted/unlock_if_necessary_test.dart

 // Copyright (c) 2012, 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.
 
 library pub_tests;
 
 import 'dart:io';
 
 import '../../test_pub.dart';
 import '../../../../../pkg/unittest/lib/unittest.dart';
 
 main() {
   test("updates one locked pub server package's dependencies if it's "
       "necessary", () {
     servePackages([
       package("foo", "1.0.0", [dependency("foo-dep")]),
       package("foo-dep", "1.0.0")
     ]);
 
     appDir([dependency("foo")]).scheduleCreate();
 
     schedulePub(args: ['install'],
-        output: const RegExp(r"Dependencies installed!$"));
+        output: new RegExp(r"Dependencies installed!$"));
 
     packagesDir({
       "foo": "1.0.0",
       "foo-dep": "1.0.0"
     }).scheduleValidate();
 
     servePackages([
       package("foo", "2.0.0", [dependency("foo-dep", ">1.0.0")]),
       package("foo-dep", "2.0.0")
     ]);
 
     schedulePub(args: ['update', 'foo'],
-        output: const RegExp(r"Dependencies updated!$"));
+        output: new RegExp(r"Dependencies updated!$"));
 
     packagesDir({
       "foo": "2.0.0",
       "foo-dep": "2.0.0"
     }).scheduleValidate();
 
     run();
   });
 }