Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/web_ui_extension_data.cc

 // 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.
 
 #include "content/renderer/web_ui_extension_data.h"
 
 #include "content/common/view_messages.h"
 #include "content/public/renderer/render_view.h"
 
 namespace content {
@@ skipping 21 matching lines @@
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
   return handled;
 }
 
 void WebUIExtensionData::OnSetWebUIProperty(const std::string& name,
                                             const std::string& value) {
   variable_map_[name] = value;
 }
 
+void WebUIExtensionData::OnDestruct() {
+  delete this;
+}
+
 }  // namespace content