Fix boolean conversion bug in dart2js + update JSRegExp accordingly.

tests/language/bool_condition_check_test.dart

+// Copyright (c) 2015, 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.
+
+// Check that passing `null` for a boolean typed parameter will still cause
+// a boolean conversion error when used in a condition in checked mode.
+
+import 'package:expect/expect.dart';
+
+@NoInline()
+String check({bool a, bool b}) {
+  String a_string = a ? 'a' : '';
+  String b_string = b ? 'b' : '';
+  return '$a_string$b_string';
+}
+
+class Class {
+  final String field;
+  Class({bool a: false, bool b: true}) : this.field = check(a: a, b: b);
+}
+
+main() {
+  Expect.equals('', new Class(a: null, b: null).field); /// 01: dynamic type error
+}