Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

extensions/renderer/api/automation/automation_api_helper.h

 // Copyright 2014 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 EXTENSIONS_RENDERER_API_AUTOMATION_AUTOMATION_API_HELPER_H_
 #define EXTENSIONS_RENDERER_API_AUTOMATION_AUTOMATION_API_HELPER_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "content/public/renderer/render_view_observer.h"
 
 namespace extensions {
 
 // Renderer-side implementation for chrome.automation API (for the few pieces
 // which aren't built in to the existing accessibility system).
 class AutomationApiHelper : public content::RenderViewObserver {
  public:
   explicit AutomationApiHelper(content::RenderView* render_view);
   ~AutomationApiHelper() override;
 
  private:
   // RenderViewObserver implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() override;
 
   void OnQuerySelector(int acc_obj_id,
                        int request_id,
                        const base::string16& selector);
 
   DISALLOW_COPY_AND_ASSIGN(AutomationApiHelper);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_API_AUTOMATION_AUTOMATION_API_HELPER_H_