Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/pepper/pepper_browser_connection.h

 // Copyright 2013 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_PEPPER_PEPPER_BROWSER_CONNECTION_H_
 #define CONTENT_RENDERER_PEPPER_PEPPER_BROWSER_CONNECTION_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 42 matching lines @@
   // Called when the renderer creates an in-process instance.
   void DidCreateInProcessInstance(PP_Instance instance,
                                   int render_frame_id,
                                   const GURL& document_url,
                                   const GURL& plugin_url);
 
   // Called when the renderer deletes an in-process instance.
   void DidDeleteInProcessInstance(PP_Instance instance);
 
  private:
+  // RenderFrameObserver implementation.
+  void OnDestruct() override;
+
   // Message handlers.
   void OnMsgCreateResourceHostsFromHostReply(
       int32_t sequence_number,
       const std::vector<int>& pending_resource_host_ids);
 
   // Return the next sequence number.
   int32_t GetNextSequence();
 
   // Sequence number to track pending callbacks.
   int32_t next_sequence_number_;
 
   // Maps a sequence number to the callback to be run.
   std::map<int32_t, PendingResourceIDCallback> pending_create_map_;
   DISALLOW_COPY_AND_ASSIGN(PepperBrowserConnection);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_PEPPER_PEPPER_BROWSER_CONNECTION_H_