Report compile-time error when extending, mixing in or implementing a malformed type.

tests/language/mixin_invalid_inheritance2_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 C<T> = Object with Malformed;  /// 01: compile-time error
+class C<T> = Object with T;  /// 02: compile-time error
+class C<T> = OBject with T<int>;  /// 03: compile-time error
+
+main() {
+  new C<C>();  /// 01: continued
+  new C<C>();  /// 02: continued
+  new C<C>();  /// 03: continued
+}