Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/presentation/presentation_dispatcher.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 CONTENT_RENDERER_PRESENTATION_PRESENTATION_DISPATCHER_H_
 #define CONTENT_RENDERER_PRESENTATION_PRESENTATION_DISPATCHER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 76 matching lines @@
       const blink::WebString& availabilityUrl,
       blink::WebPresentationAvailabilityCallbacks* callbacks) override;
   void startListening(blink::WebPresentationAvailabilityObserver*) override;
   void stopListening(blink::WebPresentationAvailabilityObserver*) override;
   void setDefaultPresentationUrl(const blink::WebString& url) override;
 
   // RenderFrameObserver implementation.
   void DidCommitProvisionalLoad(
       bool is_new_navigation,
       bool is_same_page_navigation) override;
+  void OnDestruct() override;
 
   // blink::mojom::PresentationServiceClient
   void OnScreenAvailabilityNotSupported(const mojo::String& url) override;
   void OnScreenAvailabilityUpdated(const mojo::String& url,
                                    bool available) override;
   void OnConnectionStateChanged(
       blink::mojom::PresentationSessionInfoPtr connection,
       blink::mojom::PresentationConnectionState state) override;
   void OnConnectionClosed(
       blink::mojom::PresentationSessionInfoPtr connection,
@@ skipping 59 matching lines @@
   // Updates the listening state of availability for |status| and notifies the
   // client.
   void UpdateListeningState(AvailabilityStatus* status);
 
   DISALLOW_COPY_AND_ASSIGN(PresentationDispatcher);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_PRESENTATION_PRESENTATION_DISPATCHER_H_