Add type info to fix analyzer failures for 1.23.0-dev.5.0

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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/analyzer.dart' hide Configuration;
 import 'package:async/async.dart';
 import 'package:path/path.dart' as p;
@@ skipping 146 matching lines @@
       yield new LoadSuite(name, platformConfig, () async {
         var memo = _platformPlugins[platform];
 
         try {
           var plugin = await memo.runOnce(_platformCallbacks[platform]);
           var suite = await plugin.load(path, platform, platformConfig);
           _suites.add(suite);
           return suite;
         } catch (error, stackTrace) {
           if (error is LoadException) rethrow;
-          await new Future.error(new LoadException(path, error), stackTrace);
+          await new Future.error(
+              new LoadException(path, error), stackTrace);
+          return null;
         }
       }, path: path, platform: platform);
     }
   }
 
   Future closeEphemeral() async {
     await Future.wait(_platformPlugins.values.map((memo) async {
       if (!memo.hasRun) return;
       await (await memo.future).closeEphemeral();
     }));
   }
 
   /// Closes the loader and releases all resources allocated by it.
   Future close() => _closeMemo.runOnce(() async {
     await Future.wait([
       Future.wait(_platformPlugins.values.map((memo) async {
         if (!memo.hasRun) return;
         await (await memo.future).close();
       })),
       Future.wait(_suites.map((suite) => suite.close()))
     ]);
 
     _platformPlugins.clear();
     _platformCallbacks.clear();
     _suites.clear();
   });
   final _closeMemo = new AsyncMemoizer();
 }