Revert "Remove NullPointerException."

runtime/lib/regexp_patch.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.
 
 patch class RegExp {
   /* patch */ factory RegExp(String pattern,
                              {bool multiLine: false,
                               bool ignoreCase: false}) {
     return new _JSSyntaxRegExp(pattern,
                                multiLine: multiLine,
@@ skipping 59 matching lines @@
 
   Match firstMatch(String str) {
     List match = _ExecuteMatch(str, 0);
     if (match == null) {
       return null;
     }
     return new _JSRegExpMatch(this, str, match);
   }
 
   Iterable<Match> allMatches(String str) {
-    if (str is! String) throw new ArgumentError(str);
     List<Match> result = new List<Match>();
     int length = str.length;
     int startIndex = 0;
     while (true) {
       List match = _ExecuteMatch(str, startIndex);
       if (match == null) {
         break;
       }
       result.add(new _JSRegExpMatch(this, str, match));
       int endIndex = match[1];
@@ skipping 25 matching lines @@
 
   bool get multiLine native "JSSyntaxRegExp_multiLine";
 
   bool get ignoreCase native "JSSyntaxRegExp_ignoreCase";
 
   int get _groupCount native "JSSyntaxRegExp_getGroupCount";
 
   List _ExecuteMatch(String str, int start_index)
       native "JSSyntaxRegExp_ExecuteMatch";
 }