Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

components/printing/renderer/print_web_view_helper.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_PRINTING_RENDERER_PRINT_WEB_VIEW_HELPER_H_
 #define COMPONENTS_PRINTING_RENDERER_PRINT_WEB_VIEW_HELPER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 148 matching lines @@
     PRINT_PREVIEW_USER_INITIATED_SELECTION,
     PRINT_PREVIEW_USER_INITIATED_CONTEXT_NODE,
     PRINT_PREVIEW_SCRIPTED  // triggered by window.print().
   };
 
   // RenderViewObserver implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
   void PrintPage(blink::WebLocalFrame* frame, bool user_initiated) override;
   void DidStartLoading() override;
   void DidStopLoading() override;
+  void OnDestruct() override;
 
   // Message handlers ---------------------------------------------------------
 #if defined(ENABLE_BASIC_PRINTING)
   void OnPrintPages();
   void OnPrintForSystemDialog();
   void OnPrintForPrintPreview(const base::DictionaryValue& job_settings);
 #endif  // defined(ENABLE_BASIC_PRINTING)
 #if defined(ENABLE_PRINT_PREVIEW)
   void OnInitiatePrintPreview(bool selection_only);
   void OnPrintPreview(const base::DictionaryValue& settings);
@@ skipping 345 matching lines @@
   base::Closure on_stop_loading_closure_;
 
   base::WeakPtrFactory<PrintWebViewHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintWebViewHelper);
 };
 
 }  // namespace printing
 
 #endif  // COMPONENTS_PRINTING_RENDERER_PRINT_WEB_VIEW_HELPER_H_