Fix issue 12288: a getter also returns something.

tests/language/issue12288_test.dart

+// Copyright (c) 2013, 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.
+
+main() {
+  var parent = new Element(null);
+  var child = new Element(parent);
+  var result = child.path0.length;
+  if (result != 2) {
+    throw "Expected 2, but child.path0.length was $result";
+  }
+}
+
+class Element {
+  final Element parent;
+
+  Element(this.parent);
+
+  List<Element> get path0 {
+    if (parent == null) {
+      return <Element>[this];
+    } else {
+      var list = parent.path0;
+      list.add(this);
+      return list;
+    }
+  }
+}