Implement 'edit.getRefactoring' for rename refactoring.

pkg/analysis_server/test/services/refactoring/rename_import_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_import;
 
 import 'package:analysis_server/src/protocol2.dart';
 import 'package:analysis_testing/reflective_tests.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 10 matching lines @@
 @ReflectiveTestCase()
 class RenameImportTest extends RenameRefactoringTest {
   test_checkNewName() {
     indexTestUnit("import 'dart:async' as test;");
     _createRefactoring("import 'dart:");
     expect(refactoring.oldName, 'test');
     // null
     refactoring.newName = null;
     assertRefactoringStatus(
         refactoring.checkNewName(),
-        RefactoringProblemSeverity.ERROR,
+        RefactoringProblemSeverity.FATAL,
         expectedMessage: "Import prefix name must not be null.");
     // same
     refactoring.newName = 'test';
     assertRefactoringStatus(
         refactoring.checkNewName(),
         RefactoringProblemSeverity.FATAL,
         expectedMessage: "The new name must be different than the current name.");
     // empty
     refactoring.newName = '';
     assertRefactoringStatusOK(refactoring.checkNewName());
@@ skipping 125 matching lines @@
 }
 ''');
   }
 
   void _createRefactoring(String search) {
     ImportDirective directive =
         findNodeAtString(search, (node) => node is ImportDirective);
     createRenameRefactoringForElement(directive.element);
   }
 }