Improved the way we generate mismatch descriptions.

lib/unittest/map_matchers.dart

Index: lib/unittest/map_matchers.dart
===================================================================
--- lib/unittest/map_matchers.dart	(revision 10002)
+++ lib/unittest/map_matchers.dart	(working copy)
@@ -12,7 +12,7 @@
 
   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);
 }
@@ -30,22 +30,25 @@
 
   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;
     }
   }