Improved the way we generate mismatch descriptions.

lib/unittest/map_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.
 
 /**
  * Returns a matcher which matches maps containing the given [value].
  */
 Matcher containsValue(value) => new _ContainsValue(value);
 
 class _ContainsValue extends BaseMatcher {
   final _value;
 
   const _ContainsValue(this._value);
 
-  bool matches(item) => item.containsValue(_value);
+  bool matches(item, MatchState matchState) => item.containsValue(_value);
   Description describe(Description description) =>
       description.add('contains value ').addDescriptionOf(_value);
 }
 
 /**
  * Returns a matcher which matches maps containing the key-value pair
  * with [key] => [value].
  */
 Matcher containsPair(key, value) =>
     new _ContainsMapping(key, wrapMatcher(value));
 
 class _ContainsMapping extends BaseMatcher {
   final _key;
   final Matcher _valueMatcher;
 
   const _ContainsMapping(this._key, Matcher this._valueMatcher);
 
-  bool matches(item) =>
-      item.containsKey(_key) && _valueMatcher.matches(item[_key]);
+  bool matches(item, MatchState matchState) =>
+      item.containsKey(_key) &&
+      _valueMatcher.matches(item[_key], matchState);
 
   Description describe(Description description) {
     return description.add('contains pair ').addDescriptionOf(_key).
           add(' => ').addDescriptionOf(_valueMatcher);
   }
 
-  Description describeMismatch(item, Description mismatchDescription) {
+  Description describeMismatch(item, Description mismatchDescription,
+                               MatchState matchState, bool verbose) {
     if (!item.containsKey(_key)) {
       return mismatchDescription.addDescriptionOf(item).
           add(" doesn't contain key ").addDescriptionOf(_key);
     } else {
       mismatchDescription.add(' contains key ').addDescriptionOf(_key).
           add(' but with value ');
-      _valueMatcher.describeMismatch(item[_key], mismatchDescription);
+      _valueMatcher.describeMismatch(item[_key], mismatchDescription,
+          matchState, verbose);
       return mismatchDescription;
     }
   }
 }