Add a platform plugin infrastructure.

lib/src/runner/load_suite.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 '../../test.dart';
 import '../backend/group.dart';
 import '../backend/invoker.dart';
 import '../backend/metadata.dart';
 import '../backend/suite.dart';
 import '../backend/test.dart';
 import '../backend/test_platform.dart';
 import '../utils.dart';
 import 'load_exception.dart';
+import 'plugin/environment.dart';
 import 'runner_suite.dart';
-import 'vm/environment.dart';
 
 /// A [Suite] emitted by a [Loader] that provides a test-like interface for
 /// loading a test file.
 ///
 /// This is used to expose the current status of test loading to the user. It's
 /// important to provide users visibility into what's taking a long time and
 /// where failures occur. And since some tests may be loaded at the same time as
 /// others are run, it's useful to provide that visibility in the form of a test
 /// suite so that it can integrate well into the existing reporting interface
 /// without too much extra logic.
 ///
 /// A suite is constructed with logic necessary to produce a test suite. As with
 /// a normal test body, this logic isn't run until [LiveTest.run] is called. The
 /// suite itself is returned by [suite] once it's avaialble, but any errors or
 /// prints will be emitted through the running [LiveTest].
 class LoadSuite extends Suite implements RunnerSuite {
-  final environment = const VMEnvironment();
+  final environment = const PluginEnvironment();
   final isDebugging = false;
   final onDebugging = new StreamController<bool>().stream;
 
   /// A future that completes to the loaded suite once the suite's test has been
   /// run and completed successfully.
   ///
   /// This will return `null` if the suite is unavailable for some reason (for
   /// example if an error occurred while loading it).
   Future<RunnerSuite> get suite async => (await _suiteAndZone)?.first;
 
@@ skipping 109 matching lines @@
 
     if (liveTest.errors.isEmpty) return await suite;
 
     var error = liveTest.errors.first;
     await new Future.error(error.error, error.stackTrace);
     throw 'unreachable';
   }
 
   Future close() async {}
 }