Support initialized mixin fields across scripts

tests/language/mixin_field_initializer_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.
+// Dart test program for testing throw statement
+
+class S {
+  var s1 = good_stuff();
+  static good_stuff() => "Speyburn";
+}
+
+good_stuff() => "Glenfiddich";
+
+class M {
+  var m1 = good_stuff();
+  static good_stuff() => "Macallen";
+}
+
+class A extends S with M {
+  static good_stuff() => "Ardbeg";
+}
+
+main() {
+  var a = new A();
+  Expect.equals("Macallen", a.m1);
+  Expect.equals("Speyburn", a.s1);
+
+  var m = new M();
+  Expect.equals("Macallen", m.m1);
+}