Support general expressions as keys in literal maps.

tests/language/map_literal7_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 type arguments on constant maps.
+
+library map_literal7_test;
+
+import "package:expect/expect.dart";
+
+void main() {
+  var m1 = const {"0": 0, "1": 1};
+  Expect.isTrue(m1 is Map);
+  Expect.isTrue(m1 is Map<String,int>);
+  Expect.isTrue(m1 is Map<int,dynamic>);
+  Expect.isTrue(m1 is Map<dynamic,String>);
+
+  var m2 = const <String,int>{"0": 0, "1": 1};
+  Expect.isTrue(m2 is Map);
+  Expect.isTrue(m2 is Map<String,int>);
+  Expect.isFalse(m2 is Map<int,dynamic>);
+  Expect.isFalse(m2 is Map<dynamic,String>);
+}