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

chrome/browser/first_run/first_run_internal.h

Index: chrome/browser/first_run/first_run_internal.h
diff --git a/chrome/browser/first_run/first_run_internal.h b/chrome/browser/first_run/first_run_internal.h
index eec3cf8f27c7774fab02fa126316b06fa47ce8da..e5162b424cb38bc5f97d94b7c14822a5e01f8bdb 100644
--- a/chrome/browser/first_run/first_run_internal.h
+++ b/chrome/browser/first_run/first_run_internal.h
@@ -23,7 +23,9 @@ 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().
@@ -48,6 +50,9 @@ void SetupMasterPrefsFromInstallPrefs(
 
 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);