Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/media/android/renderer_surface_view_manager.h

 // Copyright 2016 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_MEDIA_ANDROID_RENDERER_SURFACE_VIEW_MANAGER_H_
 #define CONTENT_RENDERER_MEDIA_ANDROID_RENDERER_SURFACE_VIEW_MANAGER_H_
 
 #include "base/callback.h"
 #include "content/common/content_export.h"
 #include "content/public/renderer/render_frame_observer.h"
@@ skipping 15 matching lines @@
   // RenderFrameObserver override.
   bool OnMessageReceived(const IPC::Message& msg) override;
 
   // SurfaceManager overrides.
   void CreateFullscreenSurface(
       const gfx::Size& video_natural_size,
       const media::SurfaceCreatedCB& surface_created_cb) override;
   void NaturalSizeChanged(const gfx::Size& size) override;
 
  private:
+  // RenderFrameObserver implementation.
+  void OnDestruct() override;
+
   void OnFullscreenSurfaceCreated(int surface_id);
 
   // Set when a surface request is in progress.
   media::SurfaceCreatedCB pending_surface_created_cb_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererSurfaceViewManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_ANDROID_RENDERER_SURFACE_VIEW_MANAGER_H_