Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/web_ui_extension_data.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 CONTENT_RENDERER_WEB_UI_EXTENSION_DATA_H_
 #define CONTENT_RENDERER_WEB_UI_EXTENSION_DATA_H_
 
 #include <map>
 #include <string>
 
@@ skipping 10 matching lines @@
   explicit WebUIExtensionData(RenderView* render_view);
   ~WebUIExtensionData() override;
 
   // Returns value for a given |key|. Will return an empty string if no such key
   // exists in the |variable_map_|.
   std::string GetValue(const std::string& key) const;
 
  private:
   // RenderViewObserver implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() override;
 
   void OnSetWebUIProperty(const std::string& name, const std::string& value);
 
   std::map<std::string, std::string> variable_map_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(WebUIExtensionData);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_WEB_UI_EXTENSION_DATA_H_