Add a LiveSuite class.

lib/src/backend/invoker.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 'package:stack_trace/stack_trace.dart';
 
 import '../backend/group.dart';
 import '../frontend/expect.dart';
@@ skipping 261 matching lines @@
       runZonedWithValues(() async {
         _invokerZone = Zone.current;
         _outstandingCallbackZones.add(Zone.current);
 
         // Run the test asynchronously so that the "running" state change has
         // a chance to hit its event handler(s) before the test produces an
         // error. If an error is emitted before the first state change is
         // handled, we can end up with [onError] callbacks firing before the
         // corresponding [onStateChange], which violates the timing
         // guarantees.
+        //
+        // Using [new Future] also avoids starving the DOM or other
+        // microtask-level events.
         new Future(_test._body)
             .then((_) => removeOutstandingCallback());
 
         await _outstandingCallbacks.noOutstandingCallbacks;
         if (_timeoutTimer != null) _timeoutTimer.cancel();
 
         _controller.setState(
             new State(Status.complete, liveTest.state.result));
 
-        // Use [Timer.run] here to avoid starving the DOM or other
-        // non-microtask events.
-        Timer.run(_controller.completer.complete);
+        _controller.completer.complete();
       }, zoneValues: {
         #test.invoker: this,
         // Use the invoker as a key so that multiple invokers can have different
         // outstanding callback counters at once.
         _counterKey: outstandingCallbacksForBody,
         _closableKey: true
       },
           zoneSpecification: new ZoneSpecification(
               print: (self, parent, zone, line) => _controller.print(line)),
           onError: _handleError);
     });
   }
 }