Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/chrome_render_view_observer.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.
 
 #ifndef CHROME_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_
 #define CHROME_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 26 matching lines @@
       content::RenderView* render_view,
       web_cache::WebCacheImpl* web_cache_render_thread_observer);
   ~ChromeRenderViewObserver() override;
 
  private:
   // RenderViewObserver implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
   void DidCommitProvisionalLoad(blink::WebLocalFrame* frame,
                                 bool is_new_navigation) override;
   void Navigate(const GURL& url) override;
+  void OnDestruct() override;
 
 #if !defined(OS_ANDROID)
   void OnWebUIJavaScript(const base::string16& javascript);
 #endif
 #if defined(ENABLE_EXTENSIONS)
   void OnSetVisuallyDeemphasized(bool deemphasized);
 #endif
 #if defined(OS_ANDROID)
   void OnUpdateTopControlsState(content::TopControlsState constraints,
                                 content::TopControlsState current,
@@ skipping 11 matching lines @@
   // Owned by ChromeContentRendererClient and outlive us.
   web_cache::WebCacheImpl* web_cache_impl_;
 
   // true if webview is overlayed with grey color.
   bool webview_visually_deemphasized_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeRenderViewObserver);
 };
 
 #endif  // CHROME_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_