Adding the message writing class used for remote_security_key STDOUT communication.

remoting/host/security_key/remote_security_key_message_writer.h

Index: remoting/host/security_key/remote_security_key_message_writer.h
diff --git a/remoting/host/security_key/remote_security_key_message_writer.h b/remoting/host/security_key/remote_security_key_message_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..1566e7990eddc0227e1f616bb5d72283cf025546
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+++ b/remoting/host/security_key/remote_security_key_message_writer.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_MESSAGE_WRITER_H_
+#define REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_MESSAGE_WRITER_H_
+
+#include <string>
+
+#include "base/files/file.h"
+#include "base/macros.h"
+#include "remoting/host/security_key/security_key_message.h"
+
+namespace remoting {
+
+// Used for sending remote security key messages using a file handle.
+class RemoteSecurityKeyMessageWriter {
+ public:
+  explicit RemoteSecurityKeyMessageWriter(base::File output_file);
+  ~RemoteSecurityKeyMessageWriter();
+
+  // Writes a remote security key message w/o a payload to |output_stream_|.
+  bool WriteMessage(RemoteSecurityKeyMessageType message_type);
+
+  // Writes a remote security key message with a payload to |output_stream_|.
+  bool WriteMessageWithPayload(RemoteSecurityKeyMessageType message_type,
+                               const std::string& message_payload);
+
+ private:
+  // Writes |bytes_to_write| bytes from |message| to |output_stream_|.
+  bool WriteBytesToOutput(const char* message, int bytes_to_write);
+
+  base::File output_stream_;
+  bool write_failed_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(RemoteSecurityKeyMessageWriter);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_MESSAGE_WRITER_H_