Update unittest to new package layout.

pkg/unittest/matcher.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.
-
-/**
- * MatchState is a simple wrapper around an arbitrary object.
- * [Matcher] [matches] methods can use this to store useful
- * information upon match failures, and this information will
- * be passed to [describeMismatch]. Each [Matcher] is responsible
- * for its own use of this state, so the state created by [matches]
- * should be consistent with that expected by [describeMismatch] in
- * the same [Matcher] class, but can vary between classes. The inner
- * state, if set, will typically be a [Map] with a number of key-value
- * pairs containing relevant state information.
- */
-class MatchState {
-  var state = null;
-
-  MatchState([this.state]);
-}
-
-/**
- * BaseMatcher is the base class for all matchers. To implement a new
- * matcher, either add a class that implements from IMatcher or
- * a class that inherits from Matcher. Inheriting from Matcher has
- * the benefit that a default implementation of describeMismatch will
- * be provided.
- */
-class BaseMatcher implements Matcher {
-  const BaseMatcher();
-
-  /**
-   * Tests the matcher against a given [item]
-   * and return true if the match succeeds; false otherwise.
-   * [matchState] may be used to return additional info for
-   * the use of [describeMismatch].
-   */
-  abstract bool matches(item, MatchState matchState);
-
-  /**
-   * Creates a textual description of a matcher,
-   * by appending to [mismatchDescription].
-   */
-  abstract Description describe(Description mismatchDescription);
-
-  /**
-   * Generates a description of the matcher failed for a particular
-   * [item], by appending the description to [mismatchDescription].
-   * It does not check whether the [item] fails the match, as it is
-   * only called after a failed match. There may be additional info
-   * about the mismatch in [matchState].
-   */
-  Description describeMismatch(item, Description mismatchDescription,
-                               MatchState matchState, bool verbose) =>
-    mismatchDescription.add('was ').addDescriptionOf(item);
-}