Add method flush to output stream

tests/standalone/src/io/FileOutputStreamTest.dart

Index: tests/standalone/src/io/FileOutputStreamTest.dart
diff --git a/tests/standalone/src/io/FileOutputStreamTest.dart b/tests/standalone/src/io/FileOutputStreamTest.dart
index 89760ecde380a5b8f44cbb07154b3efd44b57a3e..1fc17af580f0656829a76251513684c61d5bc6ad 100644
--- a/tests/standalone/src/io/FileOutputStreamTest.dart
+++ b/tests/standalone/src/io/FileOutputStreamTest.dart
@@ -71,7 +71,36 @@ void testOutputStreamNoPendingWrite() {
 }
 
 
+void testOutputStreamFlush() {
+  Directory tempDirectory = new Directory('');
+
+  // Create a port for waiting on the final result of this test.
+  ReceivePort done = new ReceivePort();
+  done.receive((message, replyTo) {
+    tempDirectory.deleteSync();
+    done.close();
+  });
+
+  tempDirectory.createTempSync();
+  String fileName = "${tempDirectory.path}/test";
+  File file = new File(fileName);
+  file.createSync();
+  OutputStream x = file.openOutputStream();
+  x.write([65, 66, 67]);
+  x.flush();
+  x.write([68, 69, 70]);
+  x.flush();
+  x.write([71, 72, 73]);
+  x.close();
+  x.onClosed = () {
+    file.deleteSync();
+    done.toSendPort().send("done");
+  };
+}
+
+
 main() {
   testOpenOutputStreamSync();
   testOutputStreamNoPendingWrite();
+  testOutputStreamFlush();
 }