Add StreamSubscription.asFuture.

runtime/embedders/openglui/common/gl.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.
 
 library android_extension;
 import 'dart:async';
 
 // A VERY simplified DOM.
 
 class BodyElement {
@@ skipping 237 matching lines @@
     if (_onData != null && !_paused) {
       _target.addListener(_eventType, _onData);
     }
   }
 
   void _unlisten() {
     if (_onData != null) {
       _target.removeListener(_eventType, _onData);
     }
   }
+
+  Future asFuture([var futureValue]) {
+    // We just need a future that will never succeed or fail.
+    Completer completer = new Completer();
+    return completer.future;
+  }
 }
 
 class _EventStream<T extends Event> extends Stream<T> {
   final Object _target;
   final String _eventType;
 
   _EventStream(this._target, this._eventType);
 
   // DOM events are inherently multi-subscribers.
   Stream<T> asBroadcastStream() => this;
@@ skipping 928 matching lines @@
 
   // TODO(vsm): Kill.
   noSuchMethod(invocation) {
       throw new Exception('Unimplemented/unknown ${invocation.memberName}');
   }
 }
 
 var sfx_extension = 'raw';
 int _loadSample(String s) native "LoadSample";
 int _playSample(String s) native "PlaySample";