Revert "Make Zone API strong mode clean."

tests/lib_strong/async/zone_fork_test.dart

 // Copyright (c) 2013, 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.
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'dart:async';
 
 main() {
   Completer done = new Completer();
   List events = [];
 
   Expect.identical(Zone.ROOT, Zone.current);
   Zone forked;
   forked = Zone.current.fork(specification: new ZoneSpecification(fork:
       (Zone self, ZoneDelegate parent, Zone origin,
           ZoneSpecification zoneSpecification, Map mapValues) {
     // The zone is still the same as when origin.run was invoked, which
     // is the root zone. (The origin zone hasn't been set yet).
     Expect.identical(Zone.ROOT, Zone.current);
     events.add("forked.fork");
-    var descriptionRun = zoneSpecification.run;
+    Function descriptionRun = zoneSpecification.run;
     ZoneSpecification modified = new ZoneSpecification.from(zoneSpecification,
-        run: <R>(self, parent, origin, R f()) {
+        run: (self, parent, origin, f) {
       events.add("wrapped run");
       return descriptionRun(self, parent, origin, () {
         events.add("wrapped f");
         return f();
       });
     });
     return parent.fork(origin, modified, mapValues);
   }));
 
   events.add("start");
   Zone forkedChild = forked.fork(specification: new ZoneSpecification(
-      run: <R>(Zone self, ZoneDelegate parent, Zone origin, R f()) {
+      run: (Zone self, ZoneDelegate parent, Zone origin, f()) {
     events.add("executing child run");
     return parent.run(origin, f);
   }));
 
   events.add("after child fork");
   Expect.identical(Zone.ROOT, Zone.current);
 
   forkedChild.run(() {
     events.add("child run");
   });
 
   events.add("after child run");
 
   Expect.listEquals([
     "start",
     "forked.fork",
     "after child fork",
     "wrapped run",
     "executing child run",
     "wrapped f",
     "child run",
     "after child run"
   ], events);
 }