Set MethodInvocation.interfaceTarget during type inference.

pkg/front_end/testcases/inference/future_union_upwards_generic_methods.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() async {
   var /*@type=Future<B>*/ b = new Future<B>.value(new B());
   var /*@type=Future<C>*/ c = new Future<C>.value(new C());
   var /*@type=List<Future<A>>*/ lll = /*@typeArgs=Future<A>*/ [
     /*@promotedType=none*/ b,
     /*@promotedType=none*/ c
   ];
   var /*@type=List<A>*/ result =
-      await Future. /*@typeArgs=A*/ wait(/*@promotedType=none*/ lll);
-  var /*@type=List<A>*/ result2 =
-      await Future. /*@typeArgs=A*/ wait(/*@typeArgs=Future<A>*/ [
+      await Future. /*@typeArgs=A*/ /*@target=Future::wait*/ wait(
+          /*@promotedType=none*/ lll);
+  var /*@type=List<A>*/ result2 = await Future
+      . /*@typeArgs=A*/ /*@target=Future::wait*/ wait(/*@typeArgs=Future<A>*/ [
     /*@promotedType=none*/ b,
     /*@promotedType=none*/ c
   ]);
   List<A> list = /*@promotedType=none*/ result;
   list = /*@promotedType=none*/ result2;
 }
 
 class A {}
 
 class B extends A {}
 
 class C extends A {}