Adding the message definitions for the remote_security_key STDIO communication classes.

remoting/host/security_key/remote_security_key_messages.h

Index: remoting/host/security_key/remote_security_key_messages.h
diff --git a/remoting/host/security_key/remote_security_key_messages.h b/remoting/host/security_key/remote_security_key_messages.h
new file mode 100644
index 0000000000000000000000000000000000000000..d25f1dc89b4fba3e5110d0686d7a3c9e2ffa626a
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+++ b/remoting/host/security_key/remote_security_key_messages.h
@@ -0,0 +1,105 @@
+// 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_MESSAGES_H_
+#define REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_MESSAGES_H_
+
+#include <stdint.h>
+
+#include <string>
+
+#include "base/callback_forward.h"
+
+namespace remoting {
+
+// -----------------------------------------------------------------------------
+// Introduction
+// -----------------------------------------------------------------------------
+//
+// This file defines the message format and messages used to interact with the
+// remote_security_key process which is used to forward security key requests
+// to a remote client and return security key responses from the remote client.
+
+// -----------------------------------------------------------------------------
+// Message Format

[Sergey Ulanov, 2016/03/23 19:07:25]

Are you going to put formatting/parsing code in the same file? If you put both
of them in the same .cc file then all of these constants would not need to be
defined in a header. The format looks very simple, so it doesn't seem necessary
to separate parsing and formatting. 
E.g. we could have SecurityKeyMessage struct with two static method to
format/parse the message. Similar to remoting/protocol/jingle_messages.h. WDYT?

[joedow, 2016/03/24 17:48:08]

Done.

+// -----------------------------------------------------------------------------
+//
+// {Header: uint32_t}{Control Code: uint8_t}{Payload: optional, variable length}
+//
+// Header: Defines the length of the message (Control Code + Payload).

[Sergey Ulanov, 2016/03/23 19:07:25]

Specify byte order please

[joedow, 2016/03/24 17:48:08]

Done.

+// Control Code: Contains a value representing the message type.
+// Payload: An optional field of variable length.  Data being represented in
+//          this field is dependent on the message type.
+//
+// These constants are used to enforce and validate length limitations for both
+// the message fields and the message itself.
+extern const uint32_t kMaxRemoteSecurityKeyMessageByteCount;
+extern const int kRemoteSecurityKeyMessageHeaderByteCount;
+extern const int kRemoteSecurityKeyMessageControlCodeByteCount;
+extern const int kRemoteSecurityKeyMessagePayloadByteCount;
+
+// -----------------------------------------------------------------------------
+// Messages
+// -----------------------------------------------------------------------------
+
+// This message is sent to the remote_security_key process to ask it to
+// establish a connection to the Chromoting host if a security key enabled
+// session exists for the current user.
+// Payload length: 0
+extern const uint8_t kConnectToSecurityKeyEnabledSessionMsg;
+
+// This message is sent is sent by the remote_security_key process in response
+// to the request above.
+// Payload length: 1 byte bool indicating whether a connection was established.
+// True(1): A connection with the Chromoting Host is established and ready to
+//       receive security key requests to forward.
+// False(0): No security key session was found.
+extern const uint8_t kConnectToSecurityKeyEnabledSessionRsp;
+
+// This message is sent by the remote_security_key proces when an error occurs
+// while attempting to detect the existence of a Chromoting session or when to
+// establish a connection to it.
+// Payload length: variable.  If > 0 bytes, the bytes represent an error string,
+// ascii encoded and null terminated.
+extern const uint8_t kConnectToSecurityKeyEnabledSessionErr;
+
+// This message is sent to the remote_security_key process to ask it to
+// forward a security key request.
+// Payload length: > 0 bytes consisting of the security key message to forward
+// to the remote machine using Length-Value format.
+extern const uint8_t kRemoteSecurityKeyRequestMsg;
+
+// This message is sent by the remote_security_key once a response has been
+// received from the remote machine.
+// Payload length: > 0 bytes consisting of the security key response from the
+// remote machine using Length-Value format.
+extern const uint8_t kRemoteSecurityKeyRequestRsp;
+
+// This message is sent by the remote_security_key if an error occurs either in
+// sending the request data to the remote host or if an error occurs when
+// receiving the response.
+// Payload length: variable.  If > 0 bytes, the bytes represent an error string,
+// which is ascii encoded and null terminated.
+extern const uint8_t kRemoteSecurityKeyRequestErr;
+
+// This message is sent by the remote_security_key if an unknown command is sent
+// to it.
+// Payload length: 0 bytes.
+extern const uint8_t kRemoteSecurityKeyUnknownMessageErrorMsg;
+
+// This message is sent by the remote_security_key if an unexpected error occurs
+// which does not conform to any existing category.  No response to this message
+// is expected.
+// Payload length: variable.  If > 0 bytes, the bytes represent an error string,
+// which is ascii encoded and null terminated.
+extern const uint8_t kRemoteSecurityKeyUnknownErrorMsg;
+
+// Used to pass remote security key message data between classes.
+typedef base::Callback<void(uint8_t message_type,
+                            const std::string& message_payload)>
+    RemoteSecurityKeyMessageCallback;
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_MESSAGES_H_