~Browser: Don't create TabRestoreService on exit.

chrome/browser/sessions/session_service_factory.h

Index: chrome/browser/sessions/session_service_factory.h
diff --git a/chrome/browser/sessions/session_service_factory.h b/chrome/browser/sessions/session_service_factory.h
index ed7b14b45ed35659b68215a3af6870bd31c1299d..70bdfd3f340ef04a5cf4567503570b6a42a73529 100644
--- a/chrome/browser/sessions/session_service_factory.h
+++ b/chrome/browser/sessions/session_service_factory.h
@@ -21,13 +21,14 @@ class SessionServiceFactory : public ProfileKeyedServiceFactory {
   // service hasn't yet been created, this forces creation of the session
   // service.
   //
-  // This returns NULL in two situations: the profile is incognito, or the
-  // session service has been explicitly shutdown (browser is exiting). Callers
-  // should always check the return value for NULL.
+  // This returns NULL if the profile is incognito. Callers should always check
+  // the return value for NULL.
   static SessionService* GetForProfile(Profile* profile);
 
   // Returns the session service for |profile|, but do not create it if it
-  // doesn't exist.
+  // doesn't exist. This returns NULL if the profile is incognito or if session
+  // service has been explicitly shutdown (browser is exiting). Callers should
+  // always check the return value for NULL.
   static SessionService* GetForProfileIfExisting(Profile* profile);
 
   // If |profile| has a session service, it is shut down. To properly record the