Add StreamSubscription.asFuture.

sdk/lib/async/stream_impl.dart

Index: sdk/lib/async/stream_impl.dart
diff --git a/sdk/lib/async/stream_impl.dart b/sdk/lib/async/stream_impl.dart
index e6de3d7dc38c073531119041c2bbee913ef0cfc0..fd7d7db3a8e5b59d0f9239a8258a77e4a68c5296 100644
--- a/sdk/lib/async/stream_impl.dart
+++ b/sdk/lib/async/stream_impl.dart
@@ -955,6 +955,19 @@ class _StreamSubscriptionImpl<T> extends _StreamListener<T>
     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.