Add a platform plugin infrastructure.

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';
+import '../runner/load_suite.dart';
 import '../utils.dart';
 import 'closed_exception.dart';
 import 'live_test.dart';
 import 'live_test_controller.dart';
 import 'metadata.dart';
 import 'operating_system.dart';
 import 'outstanding_callback_counter.dart';
 import 'state.dart';
 import 'suite.dart';
 import 'test.dart';
@@ skipping 218 matching lines @@
     } else if (liveTest.state.result != Result.error) {
       _controller.setState(const State(Status.complete, Result.failure));
     }
 
     _controller.addError(error, stackTrace);
     removeAllOutstandingCallbacks();
 
     // If a test was marked as success but then had an error, that indicates
     // that it was poorly-written and could be flaky.
     if (!afterSuccess) return;
+
+    // However, users don't think of load tests as "tests", so the error isn't
+    // helpful for them.
+    //
+    // TODO(nweiz): Find a way of avoiding this error that doesn't require
+    // Invoker to refer to a class from the runner.
+    if (liveTest.suite is LoadSuite) return;
+
     _handleError(
         "This test failed after it had already completed. Make sure to use "
             "[expectAsync]\n"
         "or the [completes] matcher when testing async code.",
         stackTrace);
   }
 
   /// The method that's run when the test is started.
   void _onRun() {
     _controller.setState(const State(Status.running, Result.success));
@@ skipping 29 matching lines @@
         // outstanding callback counters at once.
         _counterKey: outstandingCallbacksForBody,
         _closableKey: true
       },
           zoneSpecification: new ZoneSpecification(
               print: (self, parent, zone, line) => _controller.print(line)),
           onError: _handleError);
     });
   }
 }