Implement override-based type inference for instance methods.

pkg/front_end/testcases/inference/future_then_5.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';
 
 class MyFuture<T> implements Future<T> {
   MyFuture() {}
   MyFuture.value(T x) {}
-  dynamic noSuchMethod(invocation);
+  dynamic noSuchMethod(/*@topType=Invocation*/ invocation);
   MyFuture<S> then<S>(FutureOr<S> f(T x), {Function onError}) => null;
 }
 
 void test() {
   Future f;
   Future<int> t1 = f. /*@typeArgs=int*/ /*@target=Future::then*/ then(
       /*@returnType=Future<int>*/ (/*@type=dynamic*/ _) async =>
           await new MyFuture<int>.value(3));
   Future<int> t2 = f. /*@typeArgs=int*/ /*@target=Future::then*/ then(
       /*@returnType=Future<int>*/ (/*@type=dynamic*/ _) async {
@@ skipping 15 matching lines @@
   Future<int> t7 = f. /*@typeArgs=int*/ /*@target=Future::then*/ then(
       /*@returnType=Future<int>*/ (/*@type=dynamic*/ _) async =>
           new MyFuture<int>.value(3));
   Future<int> t8 = f. /*@typeArgs=int*/ /*@target=Future::then*/ then(
       /*@returnType=Future<int>*/ (/*@type=dynamic*/ _) async {
     return new MyFuture<int>.value(3);
   });
 }
 
 main() {}