Use default values of named arguments when invoking the default super constructor.

tests/language/src/CompileTimeConstantPTest.dart

+// 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.
+
+class A {
+  const A(
+    this.x  /// 01: compile-time error
+  );
+  final x;
+}
+
+class B extends A {
+}
+
+var b = const B();
+
+main() {
+  Expect.equals(null, b.x);
+}