Fix boolean conversion bug in dart2js + update JSRegExp accordingly.

tests/corelib/regexp/default_arguments_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.
+
+// Test that `null` is interpreted as `false` when passed as argument to
+// `caseSensitive` and `multiLine`.
+
+import 'package:expect/expect.dart';
+
+main() {
+  testCaseSensitive();
+  testMultiLine();
+}
+
+testCaseSensitive() {
+  var r1 = new RegExp('foo');
+  var r2 = new RegExp('foo', caseSensitive: true);
+  var r3 = new RegExp('foo', caseSensitive: false);
+  var r4 = new RegExp('foo', caseSensitive: null);
+  Expect.isNull(r1.firstMatch('Foo'), "r1.firstMatch('Foo')");
+  Expect.isNull(r2.firstMatch('Foo'), "r2.firstMatch('Foo')");
+  Expect.isNotNull(r3.firstMatch('Foo'), "r3.firstMatch('Foo')");
+  Expect.isNotNull(r4.firstMatch('Foo'), "r4.firstMatch('Foo')");
+}
+
+testMultiLine() {
+  var r1 = new RegExp(r'^foo$');
+  var r2 = new RegExp(r'^foo$', multiLine: true);
+  var r3 = new RegExp(r'^foo$', multiLine: false);
+  var r4 = new RegExp(r'^foo$', multiLine: null);
+  Expect.isNull(r1.firstMatch('\nfoo\n'), "r1.firstMatch('\\nfoo\\n')");
+  Expect.isNotNull(r2.firstMatch('\nfoo\n'), "r2.firstMatch('\\nfoo\\n')");
+  Expect.isNull(r3.firstMatch('\nfoo\n'), "r3.firstMatch('\\nfoo\\n')");
+  Expect.isNull(r4.firstMatch('\nfoo\n'), "r4.firstMatch('\\nfoo\\n')");
+}