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";
+
+/// Returns its argument.
+///
+/// Prevents static optimizations and inlining.
+confuse(x) {
+  // DateTime.now() cannot be predicted statically.
+  if (new DateTime.now() == 42) return confuse(2);
+  return x;
+}
+
+main() {
+  // Make sure that const maps use the == operator and not identical. The
+  // specification does not explicitly require it, but otherwise ints and
+  // Strings wouldn't make much sense as keys.
+  var m = const { 1: 42, "foo": 499 };
+  Expect.equals(42, m[confuse(1.0)]);
+  Expect.equals(499, m[confuse(new String.fromCharCodes("foo".runes))]);
+}