Fix VM to accept literal function type as type bound (fixes #29481).

tests/language/regress_29481_test.dart

+// Copyright (c) 2017, 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.
+//
+// VMOptions=--generic-method-syntax
+
+class C<T extends num Function(num)> {
+  final T func;
+  C(this.func);
+}
+
+main() {
+  var c = new C<int Function(int)>((int x) => x * 2);
+  print(c.func(21));
+}