Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/media/midi_dispatcher.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_MEDIA_MIDI_DISPATCHER_H_
 #define CONTENT_RENDERER_MEDIA_MIDI_DISPATCHER_H_
 
 #include "base/id_map.h"
 #include "base/macros.h"
 #include "content/public/renderer/render_frame_observer.h"
@@ skipping 10 matching lines @@
 // system exclusive messages.
 // It works as RenderFrameObserver to keep a 1:1 relationship with a RenderFrame
 // and make sure it has the same life cycle.
 class MidiDispatcher : public RenderFrameObserver,
                        public blink::WebMIDIClient {
  public:
   explicit MidiDispatcher(RenderFrame* render_frame);
   ~MidiDispatcher() override;
 
  private:
+  // RenderFrameObserver implementation.
+  void OnDestruct() override;
+
   // blink::WebMIDIClient implementation.
   void requestPermission(const blink::WebMIDIPermissionRequest& request,
                          const blink::WebMIDIOptions& options) override;
   void cancelPermissionRequest(
       const blink::WebMIDIPermissionRequest& request) override;
 
   // Permission for using MIDI system has been set.
   void OnPermissionSet(int request_id, blink::mojom::PermissionStatus status);
 
   // Each WebMIDIPermissionRequest object is valid until
   // cancelSysexPermissionRequest() is called with the object, or used to call
   // WebMIDIPermissionRequest::setIsAllowed().
   typedef IDMap<blink::WebMIDIPermissionRequest, IDMapOwnPointer> Requests;
   Requests requests_;
 
   blink::mojom::PermissionServicePtr permission_service_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiDispatcher);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MIDI_DISPATCHER_H_