Implement override-based type inference for instance methods.

pkg/front_end/testcases/inference/infer_types_on_generic_instantiations_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;
 
 abstract class I<E> {
-  String m(a, String f(v, E e));
+  String m(/*@topType=dynamic*/ a, String f(v, E e));
 }
 
 abstract class A<E> implements I<E> {
   const A();
-  String m(a, String f(v, E e));
+  String m(/*@topType=dynamic*/ a, String f(v, E e));
 }
 
 abstract class M {
   final int y = 0;
 }
 
 class B<E> extends A<E> implements M {
   const B();
   int get y => 0;
 
-  m(a, f(v, E e)) {}
+  /*@topType=String*/ m(/*@topType=dynamic*/ a, f(v, E e)) {}
 }
 
 foo() {
   int y = /*error:INVALID_ASSIGNMENT*/ new /*@typeArgs=dynamic*/ B()
       . /*@target=B::m*/ m(null, null);
   String z = new /*@typeArgs=dynamic*/ B(). /*@target=B::m*/ m(null, null);
 }
 
 main() {}