Use async/await in refactorings.

pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart

Index: pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
index caecadd8156203cbbc45cf2bc19b5724092d8fda..544b79aa6419358232aefa4bab03f6cdb8d85642 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
@@ -50,17 +50,16 @@ class RenameConstructorRefactoringImpl extends RenameRefactoringImpl {
   }
 
   @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) {