Make Zone API strong mode clean.

tests/lib_strong/async/future_timeout_test.dart

 // Copyright (c) 2011, 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.
 
 library future_timeout_test;
 
 import 'dart:async';
 import 'package:unittest/unittest.dart';
 
 main() {
@@ skipping 137 matching lines @@
     Zone forked;
     int registerCallDelta = 0;
     bool callbackCalled = false;
     Function callback = () {
       expect(callbackCalled, false);
       callbackCalled = true;
       expect(Zone.current, forked);
       return 42;
     };
     forked = Zone.current.fork(specification: new ZoneSpecification(
-        registerCallback: (Zone self, ZoneDelegate parent, Zone origin, f()) {
+        registerCallback:
+            <R>(Zone self, ZoneDelegate parent, Zone origin, R f()) {
       if (!identical(f, callback)) return f;
       registerCallDelta++; // Increment calls to register.
       expect(origin, forked);
       expect(self, forked);
       return expectAsync(() {
         registerCallDelta--;
         return f();
       });
     }));
     Completer completer = new Completer();
@@ skipping 22 matching lines @@
 
   test("timeoutType", () {
     Completer completer = new Completer<int>();
     Future timedOut = completer.future.timeout(const Duration(milliseconds: 5));
     expect(timedOut, new isInstanceOf<Future<int>>());
     expect(timedOut, isNot(new isInstanceOf<Future<String>>()));
     timedOut.catchError((_) {});
     completer.complete(499);
   });
 }