Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

android_webview/renderer/aw_render_view_ext.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 ANDROID_WEBVIEW_RENDERER_AW_RENDER_VIEW_EXT_H_
 #define ANDROID_WEBVIEW_RENDERER_AW_RENDER_VIEW_EXT_H_
 
 #include "base/timer/timer.h"
 #include "content/public/renderer/render_view_observer.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace android_webview {
 
 // Render process side of AwRenderViewHostExt, this provides cross-process
 // implementation of miscellaneous WebView functions that we need to poke
 // WebKit directly to implement (and that aren't needed in the chrome app).
 class AwRenderViewExt : public content::RenderViewObserver {
  public:
   static void RenderViewCreated(content::RenderView* render_view);
 
  private:
   AwRenderViewExt(content::RenderView* render_view);
   ~AwRenderViewExt() override;
 
   // RenderViewObserver:
   void DidCommitCompositorFrame() override;
   void DidUpdateLayout() override;
+  void OnDestruct() override;
 
   void CheckContentsSize();
   void PostCheckContentsSize();
 
   gfx::Size last_sent_contents_size_;
   base::OneShotTimer check_contents_size_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(AwRenderViewExt);
 };
 
 }  // namespace android_webview
 
 #endif  // ANDROID_WEBVIEW_RENDERER_AW_RENDER_VIEW_EXT_H_