Update unittest to new package layout.

pkg/unittest/test/matchers_test.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.
 
 #library('matcherTest');
-#import('../../../pkg/unittest/unittest.dart');
+#import('../../../pkg/unittest/lib/unittest.dart');
 #source('test_utils.dart');
 
 doesNotThrow() {}
 doesThrow() { throw 'X'; }
 
 class PrefixMatcher extends BaseMatcher {
   final String _prefix;
   const PrefixMatcher(this._prefix);
   bool matches(item, MatchState matchState) {
     return item is String &&
@@ skipping 500 matching lines @@
 
   group('Predicate Matchers', () {
     test('isInstanceOf', () {
       shouldFail(0, predicate((x) => x is String, "an instance of String"),
         "Expected: an instance of String but: was <0>.");
       shouldPass('cow', predicate((x) => x is String, "an instance of String"));
     });
   });
 }