emit 'this.x' when 'super.x' accesses a field

test/codegen/language/field_super_access_test.dart

+// Copyright (c) 2016, 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.
+
+// Tests that a super call to access a field in a super class is just a normal
+// field access.
+
+import "package:expect/expect.dart";
+
+class A {
+  int y;
+}
+
+class B extends A {
+  int get x => super.y;
+  void set x(val) { super.y = val; }
+}
+
+void main() {
+  var b = new B();
+  b.x = 42;
+  Expect.equals(42, b.x);
+}