Adding the message writing class used for remote_security_key STDOUT communication.

remoting/host/setup/test_util.h

Index: remoting/host/setup/test_util.h
diff --git a/remoting/host/setup/test_util.h b/remoting/host/setup/test_util.h
index 8a40f5b6b2f409cc762cf7ea51e87d2821e48d7a..8aacaa4ce4d361cd301a3424fda3bbe0e197fad2 100644
--- a/remoting/host/setup/test_util.h
+++ b/remoting/host/setup/test_util.h
@@ -10,10 +10,18 @@
 namespace remoting {
 
 // Creates an anonymous, unidirectional pipe, returning true if successful. On
-// success, the receives ownership of both files.
+// success, the receives ownership of both files.  Uses the default buffer size
+// for the platform.
 bool MakePipe(base::File* read_file,
               base::File* write_file);
 
+// Creates an anonymous, unidirectional pipe, returning true if successful. On
+// success, the receives ownership of both files.  Uses |buffer_size_bytes| to
+// define the size of the shared buffer.
+bool MakePipe(base::File* read_file,
+              base::File* write_file,
+              unsigned int buffer_size_bytes);
+
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_SETUP_TEST_UTIL_H_