If possible, use the PathService instead of the --user-data-dir flag directly

chrome/installer/util/auto_launch_util.cc

 // 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.
 
 #include "chrome/installer/util/auto_launch_util.h"
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/path_service.h"
@@ skipping 167 matching lines @@
     if (in_background) {
       cmd_line += ASCIIToUTF16(" --");
       cmd_line += ASCIIToUTF16(switches::kNoStartupWindow);
     }
     if (in_foreground) {
       cmd_line += ASCIIToUTF16(" --");
       cmd_line += ASCIIToUTF16(switches::kAutoLaunchAtStartup);
 
       const base::CommandLine& command_line =
           *base::CommandLine::ForCurrentProcess();
       if (command_line.HasSwitch(switches::kUserDataDir)) {

[grt (UTC plus 2), 2015/03/26 18:36:22]

this is subtle, so i think it needs a comment. i suggest:
      // Propagate --user-data-dir if it was specified on the command line.
      // Retrieve the value from the PathService since some sanitation may have
      // taken place. There is no need to add it to the command line in the
      // event that the dir was overridden by Group Policy since the GP override
      // will be in force when Chrome is launched.
but feel free to reword if i'm missing something.

[noms (inactive), 2015/03/30 14:06:32]

Done.

         cmd_line += ASCIIToUTF16(" --");
         cmd_line += ASCIIToUTF16(switches::kUserDataDir);
         cmd_line += ASCIIToUTF16("=\"");
-        cmd_line +=
-            command_line.GetSwitchValuePath(switches::kUserDataDir).value();
+        base::FilePath user_data_dir;
+        PathService::Get(chrome::DIR_USER_DATA, &user_data_dir);
+        cmd_line += user_data_dir.value();
         cmd_line += ASCIIToUTF16("\"");
       }
 
       cmd_line += ASCIIToUTF16(" --");
       cmd_line += ASCIIToUTF16(switches::kProfileDirectory);
       cmd_line += ASCIIToUTF16("=\"");
       cmd_line += profile_directory;
       cmd_line += ASCIIToUTF16("\"");
     }
 
@@ skipping 31 matching lines @@
 }
 
 void DisableBackgroundStartAtLogin() {
   SetWillLaunchAtLogin(base::FilePath(),
                        ASCIIToUTF16(chrome::kInitialProfile),
                        FLAG_PRESERVE,
                        FLAG_DISABLE);
 }
 
 }  // namespace auto_launch_util