Make server use the common protocol classes

pkg/analysis_server/test/services/refactoring/naming_conventions_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.
 
-import 'package:analysis_server/protocol/protocol_generated.dart'
-    show RefactoringProblemSeverity;
 import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart'
+    show RefactoringProblemSeverity;
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'abstract_refactoring.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(NamingConventionsTest);
   });
 }
 
@@ skipping 726 matching lines @@
   void test_validateVariableName_OK_middleUnderscore() {
     assertRefactoringStatusOK(validateVariableName("new_name"));
   }
 
   void test_validateVariableName_trailingBlanks() {
     assertRefactoringStatus(
         validateVariableName("newName "), RefactoringProblemSeverity.FATAL,
         expectedMessage: "Variable name must not start or end with a blank.");
   }
 }