Fix tabs duplication when restoring last closed window.

components/sessions/core/tab_restore_service.h

Index: components/sessions/core/tab_restore_service.h
diff --git a/components/sessions/core/tab_restore_service.h b/components/sessions/core/tab_restore_service.h
index 8f68b9f0bd508b0cd3d2b313bd7c258c4bb2ef6e..a851f813e575bd07c58300d79386a21e3e993ff9 100644
--- a/components/sessions/core/tab_restore_service.h
+++ b/components/sessions/core/tab_restore_service.h
@@ -182,6 +182,9 @@ class SESSIONS_EXPORT TabRestoreService : public KeyedService {
 
   // Deletes the last session.
   virtual void DeleteLastSession() = 0;
+
+  // Returns true if we're in the process of restoring some entries.
+  virtual bool IsRestoring() const = 0;
 };
 
 // A class that is used to associate platform-specific data with