Downward inference

test/dart_codegen/expect/async/timer.dart

 part of dart.async;
  abstract class Timer {factory Timer(Duration duration, void callback()) {
   if (Zone.current == Zone.ROOT) {
     return Zone.current.createTimer(duration, callback);
     }
    return Zone.current.createTimer(duration, Zone.current.bindCallback(callback, runGuarded: true));
   }
  factory Timer.periodic(Duration duration, void callback(Timer timer)) {
   if (Zone.current == Zone.ROOT) {
     return Zone.current.createPeriodicTimer(duration, callback);
     }
-   return Zone.current.createPeriodicTimer(duration, ((__x142) => DEVC$RT.wrap((dynamic f(dynamic __u137)) {
+   return Zone.current.createPeriodicTimer(duration, ((__x133) => DEVC$RT.wrap((dynamic f(dynamic __u128)) {
     dynamic c(dynamic x0) => f(x0);
      return f == null ? null : c;
     }
-  , __x142, __t140, __t138, "Wrap", """line 80, column 19 of dart:async/timer.dart: """, __x142 is __t138))(Zone.current.bindUnaryCallback(callback, runGuarded: true)));
+  , __x133, __t131, __t129, "Wrap", """line 80, column 19 of dart:async/timer.dart: """, __x133 is __t129))(Zone.current.bindUnaryCallback(callback, runGuarded: true)));
   }
  static void run(void callback()) {
   new Timer(Duration.ZERO, callback);
   }
  void cancel();
  bool get isActive;
  external static Timer _createTimer(Duration duration, void callback());
  external static Timer _createPeriodicTimer(Duration duration, void callback(Timer timer));
 }
- typedef void __t138(Timer __u139);
- typedef dynamic __t140(dynamic __u141);
+ typedef void __t129(Timer __u130);
+ typedef dynamic __t131(dynamic __u132);