Implement complex super assignment.

tests/language/super_operator_index4_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.
+
+// Test for operator[] resolved in the super class.
+
+class A {
+  var indexField = new List(2);
+  operator[](index) => indexField[index];
+}
+
+class B extends A {
+  operator[]=(index, value) { indexField[index] = value; }
+}
+
+class C extends B {
+  test() {
+    Expect.equals(42, super[0] = 42);
+    Expect.equals(42, super[0]);
+    Expect.equals(43, super[0] += 1);
+    Expect.equals(43, super[0]);
+    Expect.equals(43, super[0]++);
+    Expect.equals(44, super[0]);
+
+    Expect.equals(2, super[0] = 2);
+    Expect.equals(2, super[0]);
+    Expect.equals(3, super[0] += 1);
+    Expect.equals(3, super[0]);
+    Expect.equals(3, super[0]++);
+    Expect.equals(4, super[0]);
+  }
+}
+
+main() {
+  new C().test();
+}