Fix tabs duplication when restoring last closed window.

components/sessions/core/tab_restore_service.h

 // Copyright 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_TAB_RESTORE_SERVICE_H_
 #define COMPONENTS_SESSIONS_CORE_TAB_RESTORE_SERVICE_H_
 
 #include <list>
 #include <string>
 #include <vector>
@@ skipping 164 matching lines @@
 
   // Loads the tabs and previous session. This does nothing if the tabs
   // from the previous session have already been loaded.
   virtual void LoadTabsFromLastSession() = 0;
 
   // Returns true if the tab entries have been loaded.
   virtual bool IsLoaded() const = 0;
 
   // 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
 // TabRestoreService::Tab. See LiveTab::GetPlatformSpecificTabData().
 class SESSIONS_EXPORT PlatformSpecificTabData {
  public:
   virtual ~PlatformSpecificTabData();
 };
 
 }  // namespace sessions
 
 #endif  // COMPONENTS_SESSIONS_CORE_TAB_RESTORE_SERVICE_H_