dart2dart: Support for all constants in new backend.

tests/language/const_local_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.
 
 import "package:expect/expect.dart";
 
-class A {
-  static int a;
-  A();
-  static foo() {
-    // Make sure 'A' is not resolved to the constructor.
-    return A.a;
-  }
+main() {
+    const a = 1;
+    Expect.equals(1, a);
+    Expect.equals(1, const A(a).a);
+    Expect.equals(1, const [const A(a)][0].a);
 }
 
-main() {
-  A.a = 42;
-  Expect.equals(42, A.foo());
+class A {
+    final a;
+    const A(this.a);
 }