Fix remoting_unittests that are failing on 32-bit linux

remoting/host/security_key/remote_security_key_ipc_constants.h

 // 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_IPC_CONSTANTS_H_
 #define REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_IPC_CONSTANTS_H_
 
 #include <string>
 
 namespace remoting {
 
 // Used to indicate an error during remote security key forwarding session.
 extern const char kRemoteSecurityKeyConnectionError[];
 
 // Returns the name of the well-known IPC server channel used to initiate a
 // remote security key forwarding session.
 const std::string& GetRemoteSecurityKeyIpcChannelName();
 
 // Sets the name of the well-known IPC server channel for testing purposes.
 void SetRemoteSecurityKeyIpcChannelNameForTest(const std::string& channel_name);
 
+// Returns a path appropriate for placing a channel name.  Without this path
+// prefix, we may not have permission on linux to bind(2) a socket to a name in
+// the current directory.
+std::string GetChannelNamePathPrefixForTest();
+
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_SECURITY_KEY_REMOTE_SECURITY_KEY_IPC_CONSTANTS_H_