dart2dart: Support for all constants in new backend.

tests/language/const_map4_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";
+
+main() {
+    var a = {1: 'a', 2: 'b', 3: 'c'};
+    var b = {1: 'a', 2: 'b', 3: 'c'};
+    Expect.equals(false, a == b);
+
+    a = const {1: 'a', 2: 'b', 3: 'c'};
+    b = const {1: 'a', 2: 'b', 3: 'c'};
+    Expect.equals(true, a == b);
+
+    a = const <num,String>{1: 'a', 2: 'b', 3: 'c'};
+    b = const {1: 'a', 2: 'b', 3: 'c'};
+    Expect.equals(false, a == b);
+
+    a = const <dynamic,dynamic>{1: 'a', 2: 'b', 3: 'c'};
+    b = const {1: 'a', 2: 'b', 3: 'c'};
+    Expect.equals(true, a == b);
+}