Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

components/page_load_metrics/renderer/metrics_render_frame_observer.h

 // Copyright 2015 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 COMPONENTS_PAGE_LOAD_METRICS_RENDERER_PAGE_LOAD_METRICS_RENDER_FRAME_OBSERVER_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_RENDERER_PAGE_LOAD_METRICS_RENDER_FRAME_OBSERVER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 15 matching lines @@
  public:
   explicit MetricsRenderFrameObserver(content::RenderFrame* render_frame);
   ~MetricsRenderFrameObserver() override;
 
   // RenderFrameObserver implementation
   void DidChangePerformanceTiming() override;
   void DidObserveLoadingBehavior(
       blink::WebLoadingBehaviorFlag behavior) override;
   void DidCommitProvisionalLoad(bool is_new_navigation,
                                 bool is_same_page_navigation) override;
+  void OnDestruct() override;
 
  private:
   // Will be null when we're not actively sending metrics.
   std::unique_ptr<PageTimingMetricsSender> page_timing_metrics_sender_;
 
   void SendMetrics();
   virtual bool ShouldSendMetrics() const;
   virtual PageLoadTiming GetTiming() const;
   virtual std::unique_ptr<base::Timer> CreateTimer() const;
   virtual bool HasNoRenderFrame() const;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsRenderFrameObserver);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_RENDERER_PAGE_LOAD_METRICS_RENDER_FRAME_OBSERVER_H_