Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/safe_browsing/threat_dom_details.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.
 //
 // ThreatDOMDetails iterates over a document's frames and gathers
 // interesting URLs such as those of scripts and frames. When done, it sends
 // them to the ThreatDetails that requested them.
 
 #ifndef CHROME_RENDERER_SAFE_BROWSING_THREAT_DOM_DETAILS_H_
 #define CHROME_RENDERER_SAFE_BROWSING_THREAT_DOM_DETAILS_H_
@@ skipping 23 matching lines @@
       std::vector<SafeBrowsingHostMsg_ThreatDOMDetails_Node>* resources);
 
  private:
   // Creates a ThreatDOMDetails for the specified RenderFrame.
   // The ThreatDOMDetails should be destroyed prior to destroying
   // the RenderFrame.
   explicit ThreatDOMDetails(content::RenderFrame* render_frame);
 
   // RenderFrameObserver implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() override;
 
   void OnGetThreatDOMDetails();
 
   DISALLOW_COPY_AND_ASSIGN(ThreatDOMDetails);
 };
 
 }  // namespace safe_browsing
 
 #endif  // CHROME_RENDERER_SAFE_BROWSING_THREAT_DOM_DETAILS_H_