Add an OutputStream.closed getter.

tests/standalone/io/file_output_stream_test.dart

Index: tests/standalone/io/file_output_stream_test.dart
diff --git a/tests/standalone/io/file_output_stream_test.dart b/tests/standalone/io/file_output_stream_test.dart
index 42d3c1e8f0fbe0497335fd4faf322a2b47475a55..75e2732a81cd9211a7c5a71a5cdb466ebbaa2bcf 100644
--- a/tests/standalone/io/file_output_stream_test.dart
+++ b/tests/standalone/io/file_output_stream_test.dart
@@ -21,8 +21,11 @@ void testOpenOutputStreamSync() {
   file.createSync();
   OutputStream x = file.openOutputStream();
   x.write([65, 66, 67]);
+  Expect.isFalse(x.closed);
   x.close();
+  Expect.isTrue(x.closed);

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

This is different from an InputStream, where we want closed() to be true only
after the onClosed handler has been called, I think.

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

Should you test that write() throws an exception here?

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

Yes, but currently it would fail that test due to a bug in _FileOutputStream
that's unrelated to this change.

   x.onClosed = () {
+    Expect.isTrue(x.closed);
     file.deleteSync();
     done.toSendPort().send("done");
   };