dart2dart: Support for all constants in new backend.

tests/language/const_global_test.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.
-// Dart test program for default constructors.
 
 import "package:expect/expect.dart";
 
-class A {
-  A() : a = 499;
+const a = 1;
 
-  var a;
+main() {
+    Expect.equals(1, a);
+    Expect.equals(1, const A(a).a);
+    Expect.equals(1, const [const A(a)][0].a);
 }
 
-class B extends A {
-  B() { Expect.equals(499, a); }
+class A {
+    final a;
+    const A(this.a);
 }
-
-main() {
-  new B();
-}