Update unittest to new package layout.

pkg/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, 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, 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,
-                               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,
-          matchState, verbose);
-      return mismatchDescription;
-    }
-  }
-}