More strong mode clean-up

pkg/analyzer/lib/src/cancelable_future.dart

 // Copyright (c) 2014, 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 analyzer.src.cancelable_future;
 
 import 'dart:async';
 
 /**
  * Type of callback called when the future returned by a CancelableCompleter
@@ skipping 230 matching lines @@
     // StreamSubscription.cancel() cancels the future.
     return _completer._outerCompleter.future.asStream();
   }
 
   @override
   void cancel() {
     _completer._cancel();
   }
 
   @override
-  Future catchError(Function onError, {bool test(Object error)}) =>
+  Future<T> catchError(Function onError, {bool test(Object error)}) =>
       _completer._outerCompleter.future.catchError(onError, test: test);
 
   @override
   Future/*<S>*/ then/*<S>*/(/*=S*/ onValue(T value), {Function onError}) =>
       _completer._outerCompleter.future.then(onValue, onError: onError);
 
   @override
   Future<T> timeout(Duration timeLimit, {onTimeout()}) {
     // TODO(paulberry): Implement this in such a way that a timeout cancels
     // the future.
@@ skipping 15 matching lines @@
 
   _WrappedFuture(this._future);
 
   @override
   Stream<T> asStream() => _future.asStream();
 
   @override
   void cancel() {}
 
   @override
-  Future catchError(Function onError, {bool test(Object error)}) =>
+  Future<T> catchError(Function onError, {bool test(Object error)}) =>
       _future.catchError(onError, test: test);
 
   @override
   Future/*<S>*/ then/*<S>*/(/*=S*/ onValue(T value), {Function onError}) =>
       _future.then(onValue, onError: onError);
 
   @override
   Future<T> timeout(Duration timeLimit, {onTimeout()}) =>
       _future.timeout(timeLimit, onTimeout: onTimeout);
 
   @override
   Future<T> whenComplete(action()) => _future.whenComplete(action);
 }