Small fixes to top level type inference.

pkg/front_end/testcases/inference/void_return_type_subtypes_dynamic.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;
 
 T run<T>(T f()) {
   print("running");
   var /*@type=run::T*/ t = f();
   print("done running");
   return t;
 }
 
 void printRunning() {
   print("running");
 }
 
 var /*@topType=dynamic*/ x = run<dynamic>(printRunning);
-var /*@topType=dynamic*/ y = /*info:USE_OF_VOID_RESULT, error:TOP_LEVEL_TYPE_ARGUMENTS*/ /*@typeArgs=void*/ run(
-    printRunning);
 
 main() {
   void printRunning() {
     print("running");
   }
 
   var /*@type=dynamic*/ x = run<dynamic>(printRunning);
   var /*@type=void*/ y = /*info:USE_OF_VOID_RESULT*/ /*@typeArgs=void*/ run(
       printRunning);
   x = 123;
   x = 'hi';
   y = /*error:INVALID_ASSIGNMENT*/ 123;
   y = /*error:INVALID_ASSIGNMENT*/ 'hi';
 }