Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language/generic_constructor_mixin_test.dart

-// Copyright (c) 2014, 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.
-
-// Test that parameter types types are checked correctly in the face of
-// mixin application upon a generic constructor.
-
-import 'checked_mode_helper.dart';
-
-class A<X> {
-  A(X x);
-}
-
-class B {}
-
-class C<Y> = A<Y> with B;
-
-void main() {
-  var v = 0;
-  checkNoDynamicTypeError(() => new C<int>(v));
-  checkDynamicTypeError(() => new C<String>(v));
-}