convert engine element setter to completion element setter

pkg/analysis_server/lib/src/computer/element.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 computer.element;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
 import 'package:analyzer/src/generated/utilities_dart.dart' as engine;
 
@@ skipping 46 matching lines @@
       sb.write(parameter.toString());
     }
     sb.write(closeOptionalString);
     return '(' + sb.toString() + ')';
   } else {
     return null;
   }
 }
 
 String _getReturnTypeString(engine.Element element) {
-  if ((element is engine.ExecutableElement)) {
-    return element.returnType.toString();
+  if (element is engine.ExecutableElement) {
+    if (element.kind == engine.ElementKind.SETTER) {
+      return null;
+    } else {
+      return element.returnType.toString();
+    }
   } else {
     return null;
   }
 }
 
 bool _isAbstract(engine.Element element) {
   // TODO(scheglov) add isAbstract to Element API
   if (element is engine.ClassElement) {
     return element.isAbstract;
   }
@@ skipping 28 matching lines @@
 bool _isStatic(engine.Element element) {
   // TODO(scheglov) add isStatic to Element API
   if (element is engine.ExecutableElement) {
     return element.isStatic;
   }
   if (element is engine.PropertyInducingElement) {
     return element.isStatic;
   }
   return false;
 }