Use the dart:async Stream API thoroughly in Pub.

utils/pub/error_group.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.
 
 library error_group;
 
 import 'dart:async';
 
 /// An [ErrorGroup] entangles the errors of multiple [Future]s and [Stream]s
 /// with one another. This allows APIs to expose multiple [Future]s and
@@ skipping 161 matching lines @@
       if (!_isDone) _completer.complete(value);
       _isDone = true;
       _group._signalFutureComplete(this);
     }).catchError((error) => _group._signalError(error));
 
     // Make sure _completer.future doesn't automatically send errors to the
     // top-level.
     _completer.future.catchError((_) {});
   }
 
-  Future then(onValue(T value), {onError(AsyncError asyncError)}) {
+  Future then(onValue(value), {onError(AsyncError asyncError)}) {
     _hasListeners = true;
     return _completer.future.then(onValue, onError: onError);
   }
 
   Future catchError(onError(AsyncError asyncError), {bool test(Object error)}) {
     _hasListeners = true;
     return _completer.future.catchError(onError, test: test);
   }
 
   Future whenComplete(void action()) {
     _hasListeners = true;
     return _completer.future.whenComplete(action);
   }
 
-  Stream<T> asStream() {
+  Stream asStream() {
     _hasListeners = true;
     return _completer.future.asStream();
   }
 
   /// Signal that an error from [_group] should be propagated through [this],
   /// unless it's already complete.
   void _signalError(AsyncError error) {
     if (!_isDone) _completer.completeError(error.error, error.stackTrace);
     _isDone = true;
   }
@@ skipping 51 matching lines @@
   void _signalError(AsyncError e) {
     if (_isDone) return;
     _subscription.cancel();
     // Call these asynchronously to work around issue 7913.
     new Future.immediate(null).then((_) {
       _controller.signalError(e.error, e.stackTrace);
       _controller.close();
     });
   }
 }