Fixes possible use after free in SessionService

chrome/browser/sessions/session_service.h

Index: chrome/browser/sessions/session_service.h
diff --git a/chrome/browser/sessions/session_service.h b/chrome/browser/sessions/session_service.h
index 10c337ddadccafec743a1bf09f62e175d58c8540..8720d27385a8d84e21d3381ad00b1c28534a2f01 100644
--- a/chrome/browser/sessions/session_service.h
+++ b/chrome/browser/sessions/session_service.h
@@ -11,6 +11,7 @@
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/scoped_vector.h"
+#include "base/memory/weak_ptr.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/time/time.h"
 #include "chrome/browser/defaults.h"
@@ -493,6 +494,8 @@ class SessionService : public BaseSessionService,
   // without quitting.
   bool force_browser_not_alive_with_no_windows_;
 
+  base::WeakPtrFactory<SessionService> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(SessionService);
 };