Mark types of Constructor parameters and preserve referenced typedefs.

pkg/front_end/testcases/shaker/lib/lib.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.
 
 /// Shaker tests verify that portions of this file are preserved and that the
 /// rest is tree-shaken.
 library lib;
 
 toplevel() => null;
 
 class _A {}
 
 class B extends _A {}
 
 class C extends _A {}
 
 class K {}
 
 class M2 {}
 
 class M3 {}
 
 class M1 extends Object with M2 implements M3 {}
 
 class Bound {}
 
 class Base<T extends Bound> {}
 
-typedef T MyTypedef<T>(T arg);
+typedef T Typedef1<T>(T arg);
+
+typedef String Typedef2(int arg);
 
 class F {
   K field;
 }