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

chrome/browser/ui/startup/startup_browser_creator_browsertest.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 <algorithm>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/prefs/pref_service.h"
@@ skipping 72 matching lines @@
       other_browser = *it;
   }
   return other_browser;
 }
 
 }  // namespace
 
 class StartupBrowserCreatorTest : public ExtensionBrowserTest {
  protected:
   virtual bool SetUpUserDataDirectory() OVERRIDE {
-    // Make sure the first run sentinel file exists before running these tests,
-    // since some of them customize the session startup pref whose value can
-    // be different than the default during the first run.
-    // TODO(bauerb): set the first run flag instead of creating a sentinel file.
-    first_run::CreateSentinel();
     return ExtensionBrowserTest::SetUpUserDataDirectory();
   }
 
   virtual void SetUpCommandLine(CommandLine* command_line) OVERRIDE {
     ExtensionBrowserTest::SetUpCommandLine(command_line);
     command_line->AppendSwitch(switches::kEnablePanels);
     command_line->AppendSwitchASCII(switches::kHomePage,
                                     content::kAboutBlankURL);
 #if defined(OS_CHROMEOS)
     // TODO(nkostylev): Investigate if we can remove this switch.
@@ skipping 1269 matching lines @@
   ASSERT_EQ(1, tab_strip->count());
   EXPECT_EQ("title1.html",
             tab_strip->GetWebContentsAt(0)->GetURL().ExtractFileName());
 }
 #endif  // defined(ENABLE_CONFIGURATION_POLICY)
 
 #endif  // !defined(OS_LINUX) || !defined(GOOGLE_CHROME_BUILD) ||
         // defined(ENABLE_CONFIGURATION_POLICY)
 
 #endif  // !defined(OS_CHROMEOS)