Support general expressions as keys in literal maps.

tests/language/map_literal11_test.dart

+// Copyright (c) 2013, 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.
+
+// Test the use of reliance on identity for keys in constant maps.
+
+library map_literal11_test;
+
+import "package:expect/expect.dart";
+
+
+class A {
+  static int accessCount = 0;
+
+  final int field;
+
+  const A(this.field);
+  int get hashCode => accessCount++;
+}
+
+void main() {
+  // Non-constant map are not based on identity.
+  var m1 = {const A(0): 0, const A(1): 1, null: 2, "3": 3, 4: 4};
+  Expect.isFalse(m1.containsKey(const A(0)));
+  Expect.isFalse(m1.containsKey(const A(1)));
+  Expect.isTrue(m1.containsKey(null));
+  Expect.isTrue(m1.containsKey("3"));
+  Expect.isTrue(m1.containsKey(4));
+  Expect.isNull(m1[const A(0)]);
+  Expect.isNull(m1[const A(1)]);
+  Expect.equals(2, m1[null]);
+  Expect.equals(3, m1["3"]);
+  Expect.equals(4, m1[4]);
+
+  // Constant map are based on identity.
+  var m2 = const {const A(0): 0, const A(1): 1, null: 2, "3": 3, 4: 4};
+  Expect.isTrue(m2.containsKey(const A(0)));
+  Expect.isTrue(m2.containsKey(const A(1)));
+  Expect.isTrue(m2.containsKey(null));
+  Expect.isTrue(m2.containsKey("3"));
+  Expect.isTrue(m2.containsKey(4));
+  Expect.equals(0, m2[const A(0)]);
+  Expect.equals(1, m2[const A(1)]);
+  Expect.equals(2, m2[null]);
+  Expect.equals(3, m2["3"]);
+  Expect.equals(4, m2[4]);
+}