Convert to async/await parts that cause strong mode warnings.

pkg/analysis_server/test/edit/refactoring_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.
 
 library test.edit.refactoring;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
@@ skipping 641 matching lines @@
 }
 ''');
   }
 
   Future<Response> _computeChange() async {
     await _prepareOptions();
     // send request with the options
     return _sendExtractRequest();
   }
 
-  Future<ExtractMethodFeedback> _computeInitialFeedback() {
-    return waitForTasksFinished().then((_) {
-      return _sendExtractRequest();
-    }).then((Response response) {
-      var result = new EditGetRefactoringResult.fromResponse(response);
-      return result.feedback;
-    });
+  Future<ExtractMethodFeedback> _computeInitialFeedback() async {
+    await waitForTasksFinished();
+    Response response = await _sendExtractRequest();
+    var result = new EditGetRefactoringResult.fromResponse(response);
+    return result.feedback;
   }
 
   Future _prepareOptions() {
     return getRefactoringResult(() {
       // get initial feedback
       return _sendExtractRequest();
     }).then((result) {
       assertResultProblemsOK(result);
       // fill options from result
       ExtractMethodFeedback feedback = result.feedback;
@@ skipping 1245 matching lines @@
         .toRequest('0');
     return _assertErrorResponseNoIndex(request);
   }
 
   _assertErrorResponseNoIndex(Request request) async {
     Response response = await serverChannel.sendRequest(request);
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.NO_INDEX_GENERATED);
   }
 }