Add an OutputStream.closed getter.

runtime/bin/list_stream_impl.dart

Index: runtime/bin/list_stream_impl.dart
diff --git a/runtime/bin/list_stream_impl.dart b/runtime/bin/list_stream_impl.dart
index 8a3726e90534faee4ba1c4bf095f507ecde91d93..c752df06e96e480678a3f4b6c1f807cdfba228fc 100644
--- a/runtime/bin/list_stream_impl.dart
+++ b/runtime/bin/list_stream_impl.dart
@@ -71,6 +71,7 @@ class _ListOutputStream extends _BaseOutputStream implements ListOutputStream {
   void close() {
     if (_streamMarkedClosed) throw new StreamException.streamClosed();
     _streamMarkedClosed = true;
+    _checkScheduleCallbacks();
   }
 
   void destroy() {
@@ -144,6 +145,8 @@ class _ListOutputStream extends _BaseOutputStream implements ListOutputStream {
     }
   }
 
+  bool get closed() => _streamMarkedClosed;
+
   _BufferList _bufferList;
   bool _streamMarkedClosed = false;
   bool _closeCallbackCalled = false;