Use normal equality for const maps.

tests/language/const_map_test.dart

+// Copyright (c) 2014, 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{}
+class B{}
+
+confuse(x) {
+  if (new DateTime.now() == 42) return confuse(const { B: 42 });

[Lasse Reichstein Nielsen, 2014/02/27 08:15:34]

Type objects do implement operator==, so this should be a compile time error.
You can't use type constants in constant maps.

This is visible behavior in dart2js:

class C {}
class X<T> { T get type => T; }

const Type t1 = C;    // force it to be a compile-time constant.

main() {
 Type t2 = new X<C>().type; 
 print(identical(t1, t2));  // false
 print(t1 == t2);           // true - so "C" overrides operator==.
}

+  return x;
+}
+
+main() {
+  // Make sure that we can find types again in const maps.
+  var m = confuse(const { A: 499 });
+  Expect.equals(499, m[A]);
+  // Make sure that const maps use the == operator and not identical.
+  // Dart2js already implicitly tests this property with the type-test above.
+  m = const { 1: 42 };
+  Expect.equals(42, m[1.0]);
+}