Disallow access to static members of mixed in classes.

tests/language/mixin_illegal_static_access_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.
+
+class S {
+  static foo() => 42;
+}
+
+class M {
+  static bar() => 87;
+}
+
+typedef C = S with M;
+
+main() {
+  Expect.equals(42, S.foo());
+  Expect.equals(87, M.bar());
+
+  Expect.throws(() => C.foo(), (e) => e is NoSuchMethodError);
+  Expect.throws(() => C.bar(), (e) => e is NoSuchMethodError);
+}