Pass in `this` as a free variable to the closure class

tests/compiler/dart2js/closure/data/captured_variable.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.
 
 /*readParameterInAnonymousClosure:*/
 readParameterInAnonymousClosure(/**/ parameter) {
   return /*free=[parameter]*/ () => parameter;
 }
 
 /*readParameterInClosure:*/
@@ skipping 44 matching lines @@
 writeLocalInClosure(/**/ parameter) {
   // ignore: UNUSED_LOCAL_VARIABLE
   var /*boxed*/ local = parameter;
   /*free=[box0,local]*/ func() {
     local = 45;
   }
 
   return func;
 }
 
+class Foo {
+  int /*Foo.bar:hasThis*/ bar = 4;
+
+  /*Foo.baz:hasThis*/ baz() {
+    /*free=[this],hasThis*/ func() => bar;
+    return func;
+  }
+}
+
 main() {
   readParameterInAnonymousClosure(null);
   readParameterInClosure(null);
   writeParameterInAnonymousClosure(null);
   writeParameterInClosure(null);
   readLocalInAnonymousClosure(null);
   readLocalInClosure(null);
   writeLocalInAnonymousClosure(null);
   writeLocalInClosure(null);
+  new Foo().baz();
 }