Fix tabs duplication when restoring last closed window.

components/sessions/core/persistent_tab_restore_service.h

 // 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.
 
 #ifndef COMPONENTS_SESSIONS_CORE_PERSISTENT_TAB_RESTORE_SERVICE_H_
 #define COMPONENTS_SESSIONS_CORE_PERSISTENT_TAB_RESTORE_SERVICE_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 28 matching lines @@
   std::vector<LiveTab*> RestoreMostRecentEntry(
       LiveTabContext* context) override;
   std::unique_ptr<Tab> RemoveTabEntryById(SessionID::id_type id) override;
   std::vector<LiveTab*> RestoreEntryById(
       LiveTabContext* context,
       SessionID::id_type id,
       WindowOpenDisposition disposition) override;
   void LoadTabsFromLastSession() override;
   bool IsLoaded() const override;
   void DeleteLastSession() override;
+  bool IsRestoring() const override;
   void Shutdown() override;
 
  private:
   friend class ::PersistentTabRestoreServiceTest;
 
   class Delegate;
 
   // Exposed for testing.
   Entries* mutable_entries();
   void PruneEntries();
 
   std::unique_ptr<TabRestoreServiceClient> client_;
   std::unique_ptr<Delegate> delegate_;
   TabRestoreServiceHelper helper_;
 
   DISALLOW_COPY_AND_ASSIGN(PersistentTabRestoreService);
 };
 
 }  // namespace sessions
 
 #endif  // COMPONENTS_SESSIONS_CORE_PERSISTENT_TAB_RESTORE_SERVICE_H_