Add test that uses function.apply and mirrors in the same file.

tests/lib/mirrors/function_apply_mirrors_test.dart

+// Copyright (c) 2015, 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.
+
+// Only 'lib' imports mirrors.
+// Function.apply is resolved, before it is known that mirrors are used.
+// Dart2js has different implementations of Function.apply for different
+// emitters (like --fast-startup). Dart2js must not switch the resolved
+// Function.apply when it discovers the use of mirrors.
+// In particular it must not switch from the fast-startup emitter to the full
+// emitter without updating the Function.apply reference.
+import 'function_apply_mirrors_lib.dart' as lib;
+
+import "package:expect/expect.dart";
+
+int foo({x: 499, y: 42}) => x + y;
+
+main() {
+  Expect.equals(709, Function.apply(foo, [], {#y: 210}));
+  Expect.equals(499, lib.bar());
+}