Don't throw if a non-string is passed to RegExpMatcher.

pkg/unittest/lib/src/string_matchers.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.
 
 part of matcher;
 
 /**
  * Returns a matcher which matches if the match argument is a string and
  * is equal to [value] when compared case-insensitively.
  */
@@ skipping 160 matching lines @@
   _MatchesRegExp(re) {
     if (re is String) {
       _regexp = new RegExp(re);
     } else if (re is RegExp) {
       _regexp = re;
     } else {
       throw new ArgumentError('matches requires a regexp or string');
     }
   }
 
-  bool matches(String item, MatchState matchState) =>
-        _regexp.hasMatch(item);
+  bool matches(item, MatchState matchState) =>
+    item is String ? _regexp.hasMatch(item) : false;
 
   Description describe(Description description) =>
       description.add("match '${_regexp.pattern}'");
 }
 
 // String matchers match against a string. We add this intermediate
 // class to give better mismatch error messages than the base Matcher class.
 abstract class _StringMatcher extends BaseMatcher {
   const _StringMatcher();
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     if (!(item is String)) {
       return mismatchDescription.
           addDescriptionOf(item).
           add(' not a string');
     } else {
       return super.describeMismatch(item, mismatchDescription,
           matchState, verbose);
     }
   }
 }