Fix issue 24043: do not trust the pattern. Enable a 'hidden' test.

runtime/lib/string_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.
 
 const int _maxAscii = 0x7f;
 const int _maxLatin1 = 0xff;
 const int _maxUtf16 = 0xffff;
 const int _maxUnicode = 0x10ffff;
 
 patch class String {
@@ skipping 878 matching lines @@
     }
     int length = this.length;
     Iterator iterator = pattern.allMatches(this).iterator;
     if (length == 0 && iterator.moveNext()) {
       // A matched empty string input returns the empty list.
       return <String>[];
     }
     List<String> result = new List<String>();
     int startIndex = 0;
     int previousIndex = 0;
+    // 'pattern' may not be implemented correctly and therefore we cannot
+    // call _substringUnhchecked unless it is a trustworthy type (e.g. String).
     while (true) {
       if (startIndex == length || !iterator.moveNext()) {
-        result.add(this._substringUnchecked(previousIndex, length));
+        result.add(this.substring(previousIndex, length));
         break;
       }
       Match match = iterator.current;
       if (match.start == length) {
-        result.add(this._substringUnchecked(previousIndex, length));
+        result.add(this.substring(previousIndex, length));
         break;
       }
       int endIndex = match.end;
       if (startIndex == endIndex && endIndex == previousIndex) {
         ++startIndex;  // empty match, advance and restart
         continue;
       }
-      result.add(this._substringUnchecked(previousIndex, match.start));
+      result.add(this.substring(previousIndex, match.start));
       startIndex = previousIndex = endIndex;
     }
     return result;
   }
 
   List<int> get codeUnits => new CodeUnits(this);
 
   Runes get runes => new Runes(this);
 
   String toUpperCase() native "String_toUpperCase";
@@ skipping 389 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String input;
   final String pattern;
 }