Improve handling of invalid command line in Me2Me host.

remoting/host/host_exit_codes.h

 // Copyright (c) 2012 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_HOST_EXIT_CODES_H_
 #define REMOTING_HOST_HOST_EXIT_CODES_H_
 
 namespace remoting {
 
 // Known host exit codes. The exit codes indicating permanent errors must be in
 // sync with:
 //  - remoting/host/installer/mac/PrivilegedHelperTools/
 //      org.chromium.chromoting.me2me.sh
 //  - remoting/host/linux/linux_me2me_host.py
 enum HostExitCodes {
   // Error codes that don't indicate a permanent error condition.
   kSuccessExitCode = 0,
   kReservedForX11ExitCode = 1,
   kInitializationFailed = 2,
-  kUsageExitCode = 3,
+  kInvalidCommandLineExitCode = 3,
 
   // Error codes that do indicate a permanent error condition.
   kInvalidHostConfigurationExitCode = 100,
   kInvalidHostIdExitCode = 101,
   kInvalidOauthCredentialsExitCode = 102,
   kInvalidHostDomainExitCode = 103,
   kLoginScreenNotSupportedExitCode = 104,
   kUsernameMismatchExitCode = 105,
 
   // The range of the exit codes that should be interpreted as a permanent error
   // condition.
   kMinPermanentErrorExitCode = kInvalidHostConfigurationExitCode,
   kMaxPermanentErrorExitCode = kUsernameMismatchExitCode
 };
 
 const char* ExitCodeToString(HostExitCodes exit_code);
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_HOST_EXIT_CODES_H_