Allow binary operators on compile-time-constants.

frog/tests/leg_only/src/CompileTimeConstant4Test.dart

+// Copyright (c) 2012, 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.
+
+final x = "foo";
+final y = "foo";
+final g1 = x + "bar";
+final g2 = x + null;
+final g3 = x + 499;
+final g4 = x + 3.3;
+final g5 = x + true;
+final g6 = x + false;
+final g7 = x[0];
+final g8 = x.length;
+final g9 = x == y;
+
+main() {
+  Expect.equals("foobar", g1);
+  Expect.equals("foonull", g2);
+  Expect.equals("foo499", g3);
+  Expect.equals("foo3.3", g4);
+  Expect.equals("footrue", g5);
+  Expect.equals("foofalse", g6);
+  Expect.equals('f', g7);
+  Expect.equals(3, g8);
+  Expect.isTrue(g9);
+}