Use async/await in refactorings.

pkg/analysis_server/lib/src/services/refactoring/rename_import.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_import;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/services/correction/source_range.dart';
@@ skipping 29 matching lines @@
   }
 
   @override
   RefactoringStatus checkNewName() {
     RefactoringStatus result = super.checkNewName();
     result.addStatus(validateImportPrefixName(newName));
     return result;
   }
 
   @override
-  Future fillChange() {
+  Future fillChange() async {
     // update declaration
     {
       PrefixElement prefix = element.prefix;
       SourceEdit edit = null;
       if (newName.isEmpty) {
         int uriEnd = element.uriEnd;
         int prefixEnd = element.prefixOffset + prefix.displayName.length;
         SourceRange range = rangeStartEnd(uriEnd, prefixEnd);
         edit = newSourceEdit_range(range, "");
       } else {
         if (prefix == null) {
           SourceRange range = rangeStartLength(element.uriEnd, 0);
           edit = newSourceEdit_range(range, " as ${newName}");
         } else {
           int offset = element.prefixOffset;
           int length = prefix.displayName.length;
           SourceRange range = rangeStartLength(offset, length);
           edit = newSourceEdit_range(range, newName);
         }
       }
       if (edit != null) {
         doSourceChange_addElementEdit(change, element, edit);
       }
     }
     // update references
-    return searchEngine.searchReferences(element).then((refMatches) {
-      List<SourceReference> references = getSourceReferences(refMatches);
-      for (SourceReference reference in references) {
-        if (newName.isEmpty) {
-          reference.addEdit(change, newName);
-        } else {
-          reference.addEdit(change, "${newName}.");
-        }
+    List<SearchMatch> matches = await searchEngine.searchReferences(element);
+    List<SourceReference> references = getSourceReferences(matches);
+    for (SourceReference reference in references) {
+      if (newName.isEmpty) {
+        reference.addEdit(change, newName);
+      } else {
+        reference.addEdit(change, "${newName}.");
       }
-    });
+    }
   }
 }