Replace deprecated base::NonThreadSafe in chrome/browser/printing in favor of SequenceChecker.

chrome/browser/printing/background_printing_manager.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 CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_
 #define CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_
 
 #include <map>
 #include <memory>
 #include <set>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 namespace content {
 class WebContents;
 class BrowserContext;
 }
 
 namespace printing {
 
 // Manages hidden WebContents that prints documents in the background.
 // The hidden WebContents are no longer part of any Browser / TabStripModel.
 // The WebContents started life as a ConstrainedWebDialog.
 // They get deleted when the printing finishes.
-class BackgroundPrintingManager : public base::NonThreadSafe,
-                                  public content::NotificationObserver {
+class BackgroundPrintingManager : public content::NotificationObserver {
  public:
   class Observer;
 
   BackgroundPrintingManager();
   ~BackgroundPrintingManager() override;
 
   // Takes ownership of |preview_dialog| and deletes it when |preview_dialog|
   // finishes printing. This removes |preview_dialog| from its ConstrainedDialog
   // and hides it from the user.
   void OwnPrintPreviewDialog(content::WebContents* preview_dialog);
@@ skipping 17 matching lines @@
   // Schedule deletion of |preview_contents|.
   void DeletePreviewContents(content::WebContents* preview_contents);
 
   // A map from print preview WebContentses (managed by
   // BackgroundPrintingManager) to the Observers that observe them.
   std::map<content::WebContents*, std::unique_ptr<Observer>>
       printing_contents_map_;
 
   content::NotificationRegistrar registrar_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(BackgroundPrintingManager);
 };
 
 }  // namespace printing
 
 #endif  // CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_