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

chrome/service/cloud_print/cloud_print_proxy.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/service/cloud_print/cloud_print_proxy.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/process/kill.h"
 #include "base/process/launch.h"
 #include "base/values.h"
+#include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/cloud_print/cloud_print_constants.h"
 #include "chrome/common/cloud_print/cloud_print_proxy_info.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/service/cloud_print/print_system.h"
 #include "chrome/service/service_process.h"
 #include "chrome/service/service_process_prefs.h"
 #include "google_apis/gaia/gaia_oauth_client.h"
 #include "google_apis/google_api_keys.h"
 #include "url/gurl.h"
 
 namespace {
 
 void LaunchBrowserProcessWithSwitch(const std::string& switch_string) {
   DCHECK(g_service_process->io_thread()->message_loop_proxy()->
       BelongsToCurrentThread());
   base::FilePath exe_path;
   PathService::Get(base::FILE_EXE, &exe_path);
   if (exe_path.empty()) {
     NOTREACHED() << "Unable to get browser process binary name.";
   }
   base::CommandLine cmd_line(exe_path);
 
-  const base::CommandLine& process_command_line =

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

i think this is okay as-is since the launched process will get the value from GP
if it is overridden there. i suggest:
  // Propagate an explicit --user-data-dir value if one was given. The new
  // browser process will pick up a policy override during initialization.

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

Done.

-      *base::CommandLine::ForCurrentProcess();
-  base::FilePath user_data_dir =
-      process_command_line.GetSwitchValuePath(switches::kUserDataDir);
+  base::FilePath user_data_dir;
+  PathService::Get(chrome::DIR_USER_DATA, &user_data_dir);
   if (!user_data_dir.empty())
     cmd_line.AppendSwitchPath(switches::kUserDataDir, user_data_dir);
   cmd_line.AppendSwitch(switch_string);
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   base::Process process = base::LaunchProcess(cmd_line, base::LaunchOptions());
   if (process.IsValid())
     base::EnsureProcessGetsReaped(process.Pid());
 #else
   base::LaunchOptions launch_options;
@@ skipping 236 matching lines @@
 }
 
 void CloudPrintProxy::ShutdownBackend() {
   DCHECK(CalledOnValidThread());
   if (backend_.get())
     backend_->Shutdown();
   backend_.reset();
 }
 
 }  // namespace cloud_print