Add integration tests for postfix server api

pkg/analysis_server/test/integration/edit/test_all.dart

 // Copyright (c) 2017, 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:test_reflective_loader/test_reflective_loader.dart';
 
 import 'format_test.dart' as format_test;
 import 'get_assists_test.dart' as get_assists_test;
 import 'get_available_refactorings_test.dart'
     as get_available_refactorings_test;
 import 'get_fixes_test.dart' as get_fixes_test;
 import 'get_refactoring_test.dart' as get_refactoring_test;
+import 'get_postfix_completion_test.dart' as get_postfix_completion_test;
 import 'get_statement_completion_test.dart' as get_statement_completion_test;
+import 'is_postfix_completion_applicable_test.dart'
+    as is_postfix_completion_applicable_test;
+import 'list_postfix_completion_templates_test.dart'
+    as list_postfix_completion_templates_test;
 import 'organize_directives_test.dart' as organize_directives_test;
 import 'sort_members_test.dart' as sort_members_test;
 
 main() {
   defineReflectiveSuite(() {
     format_test.main();
     get_assists_test.main();
     get_available_refactorings_test.main();
     get_fixes_test.main();
     get_refactoring_test.main();
+    get_postfix_completion_test.main();
     get_statement_completion_test.main();
+    is_postfix_completion_applicable_test.main();
+    list_postfix_completion_templates_test.main();
     organize_directives_test.main();
     sort_members_test.main();
   }, name: 'edit');
 }