pkg/unittest: Moved `fail` to matcher library

pkg/unittest/lib/src/core_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.
 
 part of matcher;
 
 /**
  * Returns a matcher that matches empty strings, maps or iterables
  * (including collections).
  */
@@ skipping 307 matching lines @@
     this._matcher = matcher;
 
   bool matches(item, MatchState matchState) {
     if (item is! Function && item is! Future) return false;
     if (item is Future) {
       var done = wrapAsync((fn) => fn());
 
       // Queue up an asynchronous expectation that validates when the future
       // completes.
       item.then((value) {
-        done(() => expect(false, isTrue, reason:
-            "Expected future to fail, but succeeded with '$value'."));
+        done(() => fail("Expected future to fail, but succeeded with '$value'."));
       }, onError: (e) {
         done(() {
           if (_matcher == null) return;
           var reason;
           if (e.stackTrace != null) {
             var stackTrace = e.stackTrace.toString();
             stackTrace = "  ${stackTrace.replaceAll("\n", "\n  ")}";
             reason = "Actual exception trace:\n$stackTrace";
           }
           expect(e.error, _matcher, reason: reason);
@@ skipping 383 matching lines @@
       description.add(_featureDescription).add(' ').addDescriptionOf(_matcher);
 
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     mismatchDescription.add(_featureName).add(' ');
     _matcher.describeMismatch(matchState.state['feature'], mismatchDescription,
         matchState.state['innerState'], verbose);
     return mismatchDescription;
   }
 }