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

chrome/browser/chrome_browser_main.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/browser/chrome_browser_main.h"
 
 #if defined(TOOLKIT_GTK)
 #include <gtk/gtk.h>
 #endif
 
@@ skipping 1221 matching lines @@
                       "directory. This means that running multiple instances "
                       "would start multiple browser processes rather than "
                       "opening a new window in the existing process. Aborting "
                       "now to avoid profile corruption.";
         return chrome::RESULT_CODE_PROFILE_IN_USE;
 
       default:
         NOTREACHED();
     }
   }
+
+  first_run::CreateSentinelIfNeeded();
 #endif  // !defined(OS_ANDROID)
 
   // Desktop construction occurs here, (required before profile creation).
   PreProfileInit();
 
   std::string try_chrome =
       parsed_command_line().GetSwitchValueASCII(switches::kTryChromeAgain);
   if (!try_chrome.empty()) {
 #if defined(OS_WIN)
     // Setup.exe has determined that we need to run a retention experiment
@@ skipping 449 matching lines @@
   chromeos::CrosSettings::Shutdown();
 #endif
 #endif
 }
 
 // Public members:
 
 void ChromeBrowserMainParts::AddParts(ChromeBrowserMainExtraParts* parts) {
   chrome_extra_parts_.push_back(parts);
 }