Adding the RemoteSecurityKeyMessageHandler class.

remoting/host/security_key/security_key_message.cc

Index: remoting/host/security_key/security_key_message.cc
diff --git a/remoting/host/security_key/security_key_message.cc b/remoting/host/security_key/security_key_message.cc
index 571e21df06fda1761835d22e01cb5bb79c737b54..0b8b343bfdd0c7125dbeb6086287f00809f8936e 100644
--- a/remoting/host/security_key/security_key_message.cc
+++ b/remoting/host/security_key/security_key_message.cc
@@ -4,7 +4,13 @@
 
 #include "remoting/host/security_key/security_key_message.h"
 
+#include <cstdint>
+#include <string>
+#include <utility>
+
+#include "base/callback.h"
 #include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
 
 namespace {
 
@@ -49,6 +55,16 @@ RemoteSecurityKeyMessageType SecurityKeyMessage::MessageTypeFromValue(
   }
 }
 
+scoped_ptr<SecurityKeyMessage> SecurityKeyMessage::CreateMessageForTest(
+    RemoteSecurityKeyMessageType type,
+    const std::string& payload) {
+  scoped_ptr<SecurityKeyMessage> message(new SecurityKeyMessage());
+  message->type_ = type;
+  message->payload_ = payload;
+
+  return message;
+}
+
 bool SecurityKeyMessage::ParseMessage(const std::string& message_data) {
   if (!IsValidMessageSize(message_data.size())) {
     return false;