Copy JSSyntaxRegExp from frog.

dart/frog/leg/lib/regexp_helper.dart

Index: dart/frog/leg/lib/regexp_helper.dart
diff --git a/dart/frog/leg/lib/regexp_helper.dart b/dart/frog/leg/lib/regexp_helper.dart
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+++ b/dart/frog/leg/lib/regexp_helper.dart
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+// 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.
+
+class RegExpWrapper {
+  final re;
+
+  // TODO(ahe): This constructor is clearly not const. We need some
+  // better way to handle constant regular expressions. One might
+  // question if regular expressions are really constant as we have
+  // tests that expect an exception from the constructor.
+  const RegExpWrapper(pattern, multiLine, ignoreCase, global)
+    : re = makeRegExp(pattern, "${multiLine == true ? 'm' : ''}${
+                                  ignoreCase == true ? 'i' : ''}${
+                                  global == true ? 'g' : ''}");
+
+  exec(str) {
+    var result = JS('List', @'$0.exec($1)', re, checkString(str));
+    if (JS('bool', @'$0 === null', result)) return null;
+    return result;
+  }
+
+  lastIndex() => JS('List', @'$0.lastIndex', re);
+
+  test(str) => JS('List', @'$0.test($1)', re, checkString(str));
+
+  static matchStart(m) => JS('int', @'$0.index', m);
+
+  static makeRegExp(pattern, flags) {
+    checkString(pattern);
+    try {
+      return JS('Object', @'new RegExp($0, $1)', pattern, flags);
+    } catch (var e) {
+      throw new IllegalJSRegExpException(pattern,
+                                         JS('String', @'String($0)', e));
+    }
+  }
+}