Add an OutputStream.closed getter.

runtime/bin/output_stream.dart

Index: runtime/bin/output_stream.dart
diff --git a/runtime/bin/output_stream.dart b/runtime/bin/output_stream.dart
index cfbf8e51daa28c61ebbb555c7434b1ae3ff1565e..95d6569a05fc36d3d73c84c8a4e891848f5d734b 100644
--- a/runtime/bin/output_stream.dart
+++ b/runtime/bin/output_stream.dart
@@ -71,6 +71,12 @@ interface OutputStream {
   void destroy();
 
   /**
+   * Returns whether the stream is closed. No more data may be written to a

[Bill Hesse, 2012/08/08 14:21:11]

Returns whether the stream has been closed by calling close().   If true, no
more data may be written to the output stream, but there still may be buffered
data that has not been written to the communication channel.  The onClosed
handler will only be called once all data has been written out.

[nweiz, 2012/08/09 19:39:52]

Done.

+   * closed stream.
+   */
+  bool get closed();
+
+  /**
    * Sets the handler that gets called when the internal OS buffers
    * have been flushed. This callback can be used to keep the rate of
    * writing in sync with the rate the system can write data to the