Small fixes to top level type inference.

pkg/front_end/testcases/inference/downwards_inference_inside_top_level.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 A {
   B<int> b;
 }
 
 class B<T> {
   B(T x);
 }
 
 var /*@topType=A*/ t1 = new A()
   .. /*@target=A::b*/ b = new /*@typeArgs=int*/ B(1);
 var /*@topType=List<B<int>>*/ t2 = <B<int>>[new /*@typeArgs=int*/ B(2)];
-var /*@topType=List<B<dynamic>>*/ t3 = /*@typeArgs=B<dynamic>*/ [
-  new
-      /*error:TOP_LEVEL_TYPE_ARGUMENTS*/ /*@typeArgs=dynamic*/ B(3)
-];
 
 main() {}