Do not CreateSentinel until after the process singleton has been grabbed by the current process.

chrome/browser/first_run/first_run_internal.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 CHROME_BROWSER_FIRST_RUN_FIRST_RUN_INTERNAL_H_
 #define CHROME_BROWSER_FIRST_RUN_FIRST_RUN_INTERNAL_H_
 
 class MasterPrefs;
 class Profile;
 
 namespace base {
 class FilePath;
 }
 
 namespace installer {
 class MasterPreferences;
 }
 
 namespace first_run {
 
 namespace internal {
 
 enum FirstRunState {
   FIRST_RUN_UNKNOWN,  // The state is not tested or set yet.
   FIRST_RUN_TRUE,
-  FIRST_RUN_FALSE
+  FIRST_RUN_FALSE,
+  FIRST_RUN_CANCEL,  // This shouldn't be considered first run but the sentinel
+                     // should be created anyways.
 };
 
 // This variable should only be accessed through IsChromeFirstRun().
 extern FirstRunState first_run_;
 
 // Loads master preferences from the master preference file into the installer
 // master preferences. Passes the master preference file path out in
 // master_prefs_path. Returns the pointer to installer::MasterPreferences object
 // if successful; otherwise, returns NULL.
 installer::MasterPreferences* LoadMasterPrefs(
     base::FilePath* master_prefs_path);
 
 // Copies user preference file to master preference file. Returns true if
 // successful.
 bool CopyPrefFile(const base::FilePath& user_data_dir,
                   const base::FilePath& master_prefs_path);
 
 // Sets up master preferences by preferences passed by installer.
 void SetupMasterPrefsFromInstallPrefs(
     const installer::MasterPreferences& install_prefs,
     MasterPrefs* out_prefs);
 
 void SetDefaultBrowser(installer::MasterPreferences* install_prefs);
 
+// Creates the sentinel file that signals that chrome has been configured.
+bool CreateSentinel();
+
 // -- Platform-specific functions --
 
 void DoPostImportPlatformSpecificTasks(Profile* profile);
 
 // Gives the full path to the sentinel file. The file might not exist.
 // This function has a common implementation on OS_POSIX and a windows specific
 // implementation.
 bool GetFirstRunSentinelFilePath(base::FilePath* path);
 
 // This function has a common implementationin for all non-linux platforms, and
 // a linux specific implementation.
 bool IsOrganicFirstRun();
 
 // Shows the EULA dialog if required. Returns true if the EULA is accepted,
 // returns false if the EULA has not been accepted, in which case the browser
 // should exit.
 bool ShowPostInstallEULAIfNeeded(installer::MasterPreferences* install_prefs);
 
 // Returns the path for the master preferences file.
 base::FilePath MasterPrefsPath();
 
 }  // namespace internal
 }  // namespace first_run
 
 #endif  // CHROME_BROWSER_FIRST_RUN_FIRST_RUN_INTERNAL_H_