Add substitution for classes that use type variables.

tests/language/generic_creation_test.dart

 // Copyright (c) 2012, 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 A<X, Y, Z> {
   shift() => new A<Z, X, Y>();
   swap() => new A<Z, Y, X>();
   first() => new A<X, X, X>();
   last() => new A<Z, Z, Z>();
   wrap() => new A<A<X, X, X>, A<Y, Y, Y>, A<Z, Z, Z>>();
 }
 
+class B extends A<U, V, W> {}
+
+class C<T> extends A<U, T, W> {}
+
+class D<X, Y, Z> extends A<Y, Z, X> {}
+
 class U {}
 class V {}
 class W {}
 
 sameType(a, b) => Expect.equals(a.runtimeType, b.runtimeType);
 
 main() {
   A a = new A<U, V, W>();
   sameType(new A<W, U, V>(), a.shift());
   sameType(new A<W, V, U>(), a.swap());
   sameType(new A<U, U, U>(), a.first());
   sameType(new A<W, W, W>(), a.last());
   sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), a.wrap());
+  B b = new B();
+  sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), b.wrap());
+  C c = new C<V>();
+  sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), c.wrap());
+  D d = new D<U, V, W>();
+  sameType(new A<A<V, V, V>, A<W, W, W>, A<U, U, U>>(), d.wrap());
 }