Update expectations for instance creations to match front_end.

pkg/front_end/testcases/inference/constructors_infer_from_arguments_const.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.
 
 /*@testedFeatures=inference*/
 library test;
 
 class C<T> {
   final T t;
   const C(this.t);
 }
 
 main() {
-  var /*@type=C<int>*/ x = /*@typeArgs=int*/ const C(42);
+  var /*@type=C<int>*/ x = const /*@typeArgs=int*/ C(42);
 }