Refactor Future constructors.

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;
 
 deprecatedFutureValue(_FutureImpl future) =>
   future._isComplete ? future._resultOrListeners : null;
 
 
@@ skipping 121 matching lines @@
       future.catchError(handleError).then((Object value) {
         if (values == null) return null;
         values[pos] = value;
         remaining--;
         if (remaining == 0) {
           completer.complete(values);
         }
       });
     }
     if (remaining == 0) {
-      return new Future.immediate(const []);
+      return new Future.value(const []);
     }
     values = new List(remaining);
     completer = new Completer<List>();
     return completer.future;
   }
 
   Future then(f(T value), { onError(AsyncError error) }) {
     if (!_isComplete) {
       if (onError == null) {
         return new _ThenFuture(f).._subscribeTo(this);
@@ skipping 373 matching lines @@
   Future catchError(function(AsyncError error), {bool test(var error)}) {
     return _future.catchError(function, test: test);
   }
 
   Future<T> whenComplete(action()) {
     return _future.whenComplete(action);
   }
 
   Stream<T> asStream() => new Stream.fromFuture(_future);
 }