Use async/await in refactorings.

pkg/analysis_server/lib/src/services/refactoring/extract_method.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.extract_method;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
@@ skipping 151 matching lines @@
         // name
         sb.write(parameter.name);
       }
       sb.write(')');
     }
     // done
     return sb.toString();
   }
 
   @override
-  Future<RefactoringStatus> checkFinalConditions() {
+  Future<RefactoringStatus> checkFinalConditions() async {
     RefactoringStatus result = new RefactoringStatus();
     result.addStatus(validateMethodName(name));
     result.addStatus(_checkParameterNames());
-    return _checkPossibleConflicts().then((status) {
-      result.addStatus(status);
-      return result;
-    });
+    RefactoringStatus status = await _checkPossibleConflicts();
+    result.addStatus(status);
+    return result;
   }
 
 
   @override
   Future<RefactoringStatus> checkInitialConditions() {
     RefactoringStatus result = new RefactoringStatus();
     // selection
     result.addStatus(_checkSelection());
     if (result.hasFatalError) {
       return new Future.value(result);
@@ skipping 992 matching lines @@
       return false;
     }
     for (int i = 0; i < parameterTypes.length; i++) {
       if (other.parameterTypes[i] != parameterTypes[i]) {
         return false;
       }
     }
     return true;
   }
 }