Use async/await in refactorings.

pkg/analysis_server/lib/src/services/refactoring/rename_constructor.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 services.src.refactoring.rename_constructor;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
@@ skipping 32 matching lines @@
   }
 
   @override
   RefactoringStatus checkNewName() {
     RefactoringStatus result = super.checkNewName();
     result.addStatus(validateConstructorName(newName));
     return result;
   }
 
   @override
-  Future fillChange() {
+  Future fillChange() async {
     String replacement = newName.isEmpty ? '' : '.${newName}';
     // update references
-    return searchEngine.searchReferences(element).then((matches) {
-      List<SourceReference> references = getSourceReferences(matches);
-      if (!element.isSynthetic) {
-        for (SourceReference reference in references) {
-          reference.addEdit(change, replacement);
-        }
+    List<SearchMatch> matches = await searchEngine.searchReferences(element);
+    List<SourceReference> references = getSourceReferences(matches);
+    if (!element.isSynthetic) {
+      for (SourceReference reference in references) {
+        reference.addEdit(change, replacement);
       }
-    });
+    }
   }
 
   void _analyzePossibleConflicts(RefactoringStatus result) {
     // check if there are members with "newName" in the same ClassElement
     ClassElement parentClass = element.enclosingElement;
     for (Element newNameMember in getChildren(parentClass, newName)) {
       String message = format(
           "Class '{0}' already declares {1} with name '{2}'.",
           parentClass.displayName,
           getElementKindName(newNameMember),
           newName);
       result.addError(message, newLocation_fromElement(newNameMember));
     }
   }
 }