Implement super initializers.

frog/tests/leg_only/src/SuperConstructor1Test.dart

+// Copyright (c) 2011, 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.
+
+String message;
+
+class A {
+  int x;
+  A(i) : x = i {
+    message += 'A($i)';
+  }
+}
+
+class B extends A {
+  int y;
+  B(i) : y = i++, super(i + 5) {
+    message += 'B($i)';
+  }
+}
+
+class C extends B {
+  var z;
+  C(i) : super(i * 3), z = i {
+    message += 'C($i)';
+  }
+}
+
+main() {
+  message = '';
+  var c = new C(7);
+  Expect.equals(27, c.x);
+  Expect.equals(21, c.y);
+  Expect.equals(7, c.z);
+  Expect.equals('A(27)B(22)C(7)', message);
+}