Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/idle_user_detector.h

 // Copyright (c) 2011 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_IDLE_USER_DETECTOR_H_
 #define CONTENT_RENDERER_IDLE_USER_DETECTOR_H_
 
 #include "base/macros.h"
 #include "content/common/input/input_event_dispatch_type.h"
 #include "content/public/renderer/render_view_observer.h"
@@ skipping 11 matching lines @@
 // Class which observes user input events and postpones
 // idle notifications if the user is active.
 class IdleUserDetector : public RenderViewObserver {
  public:
   IdleUserDetector(RenderView* render_view);
   ~IdleUserDetector() override;
 
  private:
   // RenderViewObserver implementation:
   bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() override;
 
   void OnHandleInputEvent(const blink::WebInputEvent* event,
                           const ui::LatencyInfo& latency_info,
                           InputEventDispatchType dispatch_type);
 
   DISALLOW_COPY_AND_ASSIGN(IdleUserDetector);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_IDLE_USER_DETECTOR_H_