Support general expressions as keys in literal maps.

tests/language/map_literal6_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 general expression as keys in const map literals.
+
+library map_literal6_test;
+
+import "package:expect/expect.dart";
+
+class A {
+  const A();
+}
+class B {
+  final a;
+  const B(this.a);
+}
+
+void main() {
+  var m1 = const {
+    const A(): 0,
+    const B(0): 1,
+    const B(1): 2,
+    const B(const A()): 3,
+    const B(0): 4,
+  };
+  Expect.isTrue(m1.containsKey(const A()));
+  Expect.isTrue(m1.containsKey(const B(0)));
+  Expect.isTrue(m1.containsKey(const B(1)));
+  Expect.isTrue(m1.containsKey(const B(const A())));
+  Expect.equals(0, m1[const A()]);
+  Expect.equals(4, m1[const B(0)]);
+  Expect.equals(2, m1[const B(1)]);
+  Expect.equals(3, m1[const B(const A())]);
+}