Switch server tests to strong mode.

pkg/analysis_server/test/services/correction/assist_test.dart

 // Copyright (c) 2014, 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:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
@@ skipping 3810 matching lines @@
 ''');
     await assertHasAssistAt(
         'int ',
         DartAssistKind.REMOVE_TYPE_ANNOTATION,
         '''
 final V = 1;
 ''');
   }
 
   test_reparentFlutterList_BAD_multiLine() async {
+    verifyNoTestUnitErrors = false;
     _configureFlutterPkg({
       'src/widgets/framework.dart': flutter_framework_code,
     });
     await resolveTestUnit('''
 import 'package:flutter/src/widgets/framework.dart';
 build() {
   return new Container(
     child: new Row(
       children: [/*caret*/
 // start
@@ skipping 925 matching lines @@
 
   @override
   final AstProvider astProvider;
 
   @override
   final CompilationUnit unit;
 
   _DartAssistContextForValues(this.source, this.selectionOffset,
       this.selectionLength, this.analysisDriver, this.astProvider, this.unit);
 }