Fix crash due to AbstractFieldElement.computeType.

dart/tests/try/poi/data/abstract_field.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 interesting;
+library abstract_field;
 
-class Foo {
-  fisk() {
-  }
-  hest() {
+class A {
+  String get foo => null;
+
+  set foo(String v) => null;
+
+  method() {
   }
 }
 
+String get bar => null;
+
+set bar(String v) => null;
+
 main() {}