fixes #27586, prefer context type in generic inference

tests/language_strong/recursive_generic_test.dart

 // Copyright (c) 2016, 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.
 
 import "package:expect/expect.dart";
 
 abstract class S<T extends S<T>> { m() => 123; get S_T => T; }
 class C<T extends C<T>> extends S<C> { m() => 456; get C_T => T; }
 
+class D extends C<D> {}
+
 main() {
-  Expect.equals(new C().m(), 456);
+  Expect.equals(new C<D>().m(), 456);
   // TODO(jmesserly): this should be dart1 vs dart2, not DDC vs VM.
   var isVM = const bool.fromEnvironment('dart.isVM');
-  Expect.equals(new C().S_T.toString(), isVM ? 'C' : 'C<C>');
-  Expect.equals(new C().C_T.toString(), isVM ? 'dynamic' : 'C');
+  Expect.equals(new C<D>().S_T.toString(), isVM ? 'C' : 'C<C>');
+  Expect.equals(new C<D>().C_T.toString(), isVM ? 'dynamic' : 'D');
 }