Convert refactoring tests to use 'await'.

pkg/analysis_server/test/services/refactoring/rename_library_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.services.refactoring.rename_library;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:unittest/unittest.dart';
 
@@ skipping 28 matching lines @@
         RefactoringProblemSeverity.FATAL,
         expectedMessage: "Library name must not be blank.");
     // same name
     refactoring.newName = 'my.app';
     assertRefactoringStatus(
         refactoring.checkNewName(),
         RefactoringProblemSeverity.FATAL,
         expectedMessage: "The new name must be different than the current name.");
   }
 
-  test_createChange() {
+  test_createChange() async {
     Source unitSource = addSource('/part.dart', '''
 part of my.app;
 ''');
     indexTestUnit('''
 library my.app;
 part 'part.dart';
 ''');
     index.indexUnit(
         context,
         context.resolveCompilationUnit2(unitSource, testSource));
     // configure refactoring
     _createRenameRefactoring();
     expect(refactoring.refactoringName, 'Rename Library');
     expect(refactoring.elementKindName, 'library');
     refactoring.newName = 'the.new.name';
     // validate change
-    return assertSuccessfulRefactoring('''
+    await assertSuccessfulRefactoring('''
 library the.new.name;
 part 'part.dart';
-''').then((_) {
-      assertFileChangeResult('/part.dart', '''
+''');
+    assertFileChangeResult('/part.dart', '''
 part of the.new.name;
 ''');
-    });
   }
 
   void _createRenameRefactoring() {
     createRenameRefactoringForElement(testUnitElement.library);
   }
 }