Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/content_settings_observer.h

Index: chrome/renderer/content_settings_observer.h
diff --git a/chrome/renderer/content_settings_observer.h b/chrome/renderer/content_settings_observer.h
index f5b88c88f9ba877c850971e8bd6d739f97dfbcd4..27a304cc7a6d87c9525376eeb861d636c7a3a6ae 100644
--- a/chrome/renderer/content_settings_observer.h
+++ b/chrome/renderer/content_settings_observer.h
@@ -96,6 +96,7 @@ class ContentSettingsObserver
   bool OnMessageReceived(const IPC::Message& message) override;
   void DidCommitProvisionalLoad(bool is_new_navigation,
                                 bool is_same_page_navigation) override;
+  void OnDestruct() override;
 
   // Message handlers.
   void OnLoadBlockedPlugins(const std::string& identifier);