Fix issue 7086: support call-through getter for interceptor classes.

tests/language/interceptor5_test.dart

Index: tests/language/interceptor5_test.dart
===================================================================
--- tests/language/interceptor5_test.dart	(revision 0)
+++ tests/language/interceptor5_test.dart	(revision 0)
@@ -0,0 +1,9 @@
+// Copyright (c) 2012, 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.
+
+get X => [() => 123];
+
+main() {
+  Expect.equals(123, X.last());
+}