Minor type inference fixes.

pkg/front_end/testcases/inference/future_then_upwards_from_block.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;
 
 import 'dart:async';
 
 main() {
   Future<int> base;
   var /*@type=Future<bool>*/ f =
       base. /*@typeArgs=bool*/ /*@target=Future::then*/ then(
           /*@returnType=bool*/ (/*@type=int*/ x) {
-    return x /*@target=Object::==*/ == 0;
+    return x /*@target=num::==*/ == 0;
   });
   var /*@type=Future<bool>*/ g =
       base. /*@typeArgs=bool*/ /*@target=Future::then*/ then(
-          /*@returnType=bool*/ (/*@type=int*/ x) =>
-              x /*@target=Object::==*/ == 0);
+          /*@returnType=bool*/ (/*@type=int*/ x) => x /*@target=num::==*/ == 0);
   Future<bool> b = f;
   b = g;
 }