Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/safe_browsing/threat_dom_details.cc

 // 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.
 
 #include "chrome/renderer/safe_browsing/threat_dom_details.h"
 
 #include "base/compiler_specific.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/safe_browsing/safebrowsing_messages.h"
 #include "content/public/renderer/render_frame.h"
@@ skipping 89 matching lines @@
       if (resources->size() >= kMaxNodes) {
         // We have reached kMaxNodes, exit early.
         resources->push_back(details_node);
         return;
       }
     }
   }
   resources->push_back(details_node);
 }
 
+void ThreatDOMDetails::OnDestruct() {
+  delete this;
+}
+
 }  // namespace safe_browsing