Migrated test block 19 to Dart 2.0.

tests/corelib_2/regexp/alternative-length-miscalculation_test.dart

 // Copyright (c) 2014, the Dart project authors. All rights reserved.
 // Copyright 2013 the V8 project authors. All rights reserved.
 // Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 // 1.  Redistributions of source code must retain the above copyright
 //     notice, this list of conditions and the following disclaimer.
 // 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 17 matching lines @@
 void main() {
   description(
       "This page tests for length miscalculations in regular expression processing.");
 
   var re = new RegExp(r"b|[^b]");
   assertEquals('a'.indexOf(re, 1), -1);
 
   var re2 = new RegExp(r"[^a]|ab");
   shouldBeFalse(re2.hasMatch(''));
 }