Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/accessibility/renderer_accessibility.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 CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_
 #define CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_
 
 #include <vector>
 
 #include "base/containers/hash_tables.h"
@@ skipping 82 matching lines @@
 
   // Check the entire accessibility tree to see if any nodes have
   // changed location, by comparing their locations to the cached
   // versions. If any have moved, send an IPC with the new locations.
   void SendLocationChanges();
 
   // The RenderFrameImpl that owns us.
   RenderFrameImpl* render_frame_;
 
  private:
+  // RenderFrameObserver implementation.
+  void OnDestruct() override;
+
   // Handlers for messages from the browser to the renderer.
   void OnDoDefaultAction(int acc_obj_id);
   void OnEventsAck();
   void OnFatalError();
   void OnHitTest(gfx::Point point);
   void OnSetAccessibilityFocus(int acc_obj_id);
   void OnReset(int reset_token);
   void OnScrollToMakeVisible(int acc_obj_id, gfx::Rect subfocus);
   void OnScrollToPoint(int acc_obj_id, gfx::Point point);
   void OnSetScrollOffset(int acc_obj_id, gfx::Point offset);
@@ skipping 36 matching lines @@
 
   // So we can queue up tasks to be executed later.
   base::WeakPtrFactory<RendererAccessibility> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererAccessibility);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_