Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/stats_collection_observer.h

 // Copyright 2013 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_STATS_COLLECTION_OBSERVER_H_
 #define CONTENT_RENDERER_STATS_COLLECTION_OBSERVER_H_
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "content/public/renderer/render_view_observer.h"
@@ skipping 12 matching lines @@
   // RenderViewObserver implementation
   void DidStartLoading() override;
   void DidStopLoading() override;
 
   // Timing for the page load start and stop.  These functions may return
   // a null time value under various circumstances.
   const base::Time& load_start_time() { return start_time_; }
   const base::Time& load_stop_time() { return stop_time_; }
 
  private:
+  // RenderViewObserver implementation.
+  void OnDestruct() override;
+
   base::Time start_time_;
   base::Time stop_time_;
 
    DISALLOW_COPY_AND_ASSIGN(StatsCollectionObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_STATS_COLLECTION_OBSERVER_H_