Add generic annotations to more SDK APIs.

sdk/lib/async/future_impl.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 /** The onValue and onError handlers return either a value or a future */
 typedef dynamic _FutureOnValue<T>(T value);
 /** Test used by [Future.catchError] to handle skip some errors. */
 typedef bool _FutureErrorTest(var error);
@@ skipping 173 matching lines @@
   bool get _isChained         => _state == _CHAINED;
   bool get _isComplete        => _state >= _VALUE;
   bool get _hasError          => _state == _ERROR;
 
   void _setChained(_Future source) {
     assert(_mayAddListener);
     _state = _CHAINED;
     _resultOrListeners = source;
   }
 
-  Future then(f(T value), { Function onError }) {
+  Future/*<S>*/ then/*<S>*/(f(T value), { Function onError }) {
     Zone currentZone = Zone.current;
     if (!identical(currentZone, _ROOT_ZONE)) {
       f = currentZone.registerUnaryCallback(f);
       if (onError != null) {
         onError = _registerErrorHandler(onError, currentZone);
       }
     }
     return _thenNoZoneRegistration(f, onError);
   }
 
@@ skipping 504 matching lines @@
       }
     }, onError: (e, s) {
       if (timer.isActive) {
         timer.cancel();
         result._completeError(e, s);
       }
     });
     return result;
   }
 }