Add support for evaluating platform selectors.

lib/src/runner/loader.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.
 
 library unittest.runner.loader;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 import 'package:path/path.dart' as p;
 
 import '../backend/suite.dart';
-import '../runner/test_platform.dart';
+import '../backend/test_platform.dart';
 import '../util/dart.dart';
 import '../util/io.dart';
 import '../util/remote_exception.dart';
 import '../utils.dart';
 import 'browser/server.dart';
 import 'load_exception.dart';
 import 'vm/isolate_test.dart';
 
 /// A class for finding test files and loading them into a runnable form.
 class Loader {
@@ skipping 110 matching lines @@
   Future close() {
     for (var isolate in _isolates) {
       isolate.kill();
     }
     _isolates.clear();
 
     if (_browserServerCompleter == null) return new Future.value();
     return _browserServer.then((browserServer) => browserServer.close());
   }
 }