Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

components/dom_distiller/content/renderer/distiller_js_render_frame_observer.cc

 // 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.
 
 #include "components/dom_distiller/content/renderer/distiller_js_render_frame_observer.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "components/dom_distiller/content/common/distiller_page_notifier_service.mojom.h"
@@ skipping 49 matching lines @@
 void DistillerJsRenderFrameObserver::CreateDistillerPageNotifierService(
     mojo::InterfaceRequest<mojom::DistillerPageNotifierService> request) {
   // This is strongly bound to and owned by the pipe.
   new DistillerPageNotifierServiceImpl(this, std::move(request));
 }
 
 void DistillerJsRenderFrameObserver::SetIsDistillerPage() {
   is_distiller_page_ = true;
 }
 
+void DistillerJsRenderFrameObserver::OnDestruct() {
+  delete this;
+}
+
 }  // namespace dom_distiller