Add a dedicated Result for skipped tests.

lib/src/frontend/expect_async.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:async';
 
 import '../backend/invoker.dart';
-import '../backend/state.dart';
 import 'expect.dart';
 
 /// An object used to detect unpassed arguments.
 const _PLACEHOLDER = const Object();
 
 // Functions used to check how many arguments a callback takes.
 typedef _Func0();
 typedef _Func1(a);
 typedef _Func2(a, b);
 typedef _Func3(a, b, c);
@@ skipping 144 matching lines @@
       a3 = _PLACEHOLDER, a4 = _PLACEHOLDER, a5 = _PLACEHOLDER]) =>
       _run([a0, a1, a2, a3, a4, a5].where((a) => a != _PLACEHOLDER));
 
   /// Runs the wrapped function with [args] and returns its return value.
   _run(Iterable args) {
     // Note that in the old test, this returned `null` if it encountered an
     // error, where now it just re-throws that error because Zone machinery will
     // pass it to the invoker anyway.
     try {
       _actualCalls++;
-      if (_invoker.liveTest.isComplete &&
-          _invoker.liveTest.state.result == Result.success) {
+      if (_invoker.liveTest.state.shouldBeDone) {
         throw 'Callback ${_id}called ($_actualCalls) after test case '
               '${_invoker.liveTest.test.name} had already completed.$_reason';
       } else if (_maxExpectedCalls >= 0 && _actualCalls > _maxExpectedCalls) {
         throw new TestFailure('Callback ${_id}called more times than expected '
                               '($_maxExpectedCalls).$_reason');
       }
 
       return Function.apply(_callback, args.toList());
     } catch (error, stackTrace) {
       _zone.handleUncaughtError(error, stackTrace);
@@ skipping 56 matching lines @@
 Function expectAsyncUntil(Function callback, bool isDone(),
     {String id, String reason}) {
   if (Invoker.current == null) {
     throw new StateError(
         "expectAsyncUntil() may only be called within a test.");
   }
 
   return new _ExpectedFunction(callback, 0, -1,
       id: id, reason: reason, isDone: isDone).func;
 }