Add StreamSubscription.asFuture.

sdk/lib/async/stream_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;
 
 // States shared by single/multi stream implementations.
 
 // Completion state of the stream.
 /// Initial and default state where the stream can receive and send events.
@@ skipping 937 matching lines @@
 
   void pause([Future resumeSignal]) {
     if (!_isSubscribed) return;
     _source._pause(this, resumeSignal);
   }
 
   void resume() {
     if (!_isSubscribed || !isPaused) return;
     _source._resume(this, false);
   }
+
+  Future asFuture([var futureValue]) {
+    _FutureImpl<T> result = new _FutureImpl<T>();
+
+    // Overwrite the onDone and onError handlers.
+    onDone(() { result._setValue(futureValue); });
+    onError((AsyncError error) {
+      cancel();

[Anders Johnsen, 2013/04/15 09:15:47]

Set unsubscribeOnError = true?

[Lasse Reichstein Nielsen, 2013/04/15 10:19:15]

It's final, and if you overwrite onError again, which you still can, it won't
change back.

+      result._setError(error);
+    });
+
+    return result;
+  }
 }
 
 // Internal helpers.
 
 // Types of the different handlers on a stream. Types used to type fields.
 typedef void _DataHandler<T>(T value);
 typedef void _ErrorHandler(AsyncError error);
 typedef void _DoneHandler();
 
 
@@ skipping 361 matching lines @@
                                      onError: this._addError,
                                      onDone: this._close);
     } else {
       // TODO(lrn): Check why this can happen.
       if (_subscription == null) return;
       _subscription.cancel();
       _subscription = null;
     }
   }
 }