Firefox overlay is seen opened even if Import Overlay is Cancelled.

chrome/browser/ui/webui/settings/settings_import_data_handler.h

 // Copyright 2016 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 CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_IMPORT_DATA_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_IMPORT_DATA_HANDLER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 21 matching lines @@
   // SettingsPageUIHandler
   void RegisterMessages() override;
   void OnJavascriptAllowed() override {}
   void OnJavascriptDisallowed() override;
 
  private:
   void StartImport(const importer::SourceProfile& source_profile,
                    uint16_t imported_items);
 
   void ImportData(const base::ListValue* args);
+  void Close(const base::ListValue* args);
 
   void InitializeDialog(const base::ListValue* args);
   void SendBrowserProfileData(const std::string& callback_id);
 
   // importer::ImporterProgressObserver:
   void ImportStarted() override;
   void ImportItemStarted(importer::ImportItem item) override;
   void ImportItemEnded(importer::ImportItem item) override;
   void ImportEnded() override;
 
@@ skipping 14 matching lines @@
   bool import_did_succeed_;
 
   scoped_refptr<ui::SelectFileDialog> select_file_dialog_;
 
   DISALLOW_COPY_AND_ASSIGN(ImportDataHandler);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_IMPORT_DATA_HANDLER_H_