Properly type infer for-in loops when the iterator type is a type parameter.

pkg/front_end/testcases/inference/lambda_does_not_have_propagated_type_hint.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;
 
 List<String> getListOfString() => const <String>[];
 
 void foo() {
   List myList = getListOfString();
   myList. /*@typeArgs=int*/ /*@target=Iterable::map*/ map(
       /*@returnType=int*/ (/*@type=dynamic*/ type) => 42);
 }
 
 void bar() {
   var /*@type=dynamic*/ list;
   try {
     list = <String>[];
   } catch (_) {
     return;
   }
   /*info:DYNAMIC_INVOKE*/ list.map(
       /*@returnType=String*/ (/*@type=dynamic*/ value) => '${value}');
 }
+
+main() {}