Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/presentation/presentation_dispatcher.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 "content/renderer/presentation/presentation_dispatcher.h"
 
 #include <algorithm>
 #include <utility>
 #include <vector>
 
@@ skipping 290 matching lines @@
   blink::WebFrame* frame = render_frame()->GetWebFrame();
   // If not top-level navigation.
   if (frame->parent() || is_same_page_navigation)
     return;
 
   // Remove all pending send message requests.
   MessageRequestQueue empty;
   std::swap(message_request_queue_, empty);
 }
 
+void PresentationDispatcher::OnDestruct() {
+  delete this;
+}
+
 void PresentationDispatcher::OnScreenAvailabilityUpdated(
     const mojo::String& url, bool available) {
   const std::string& availability_url = url.get();
   auto status_it = availability_status_.find(availability_url);
   if (status_it == availability_status_.end())
     return;
   AvailabilityStatus* status = status_it->second.get();
   DCHECK(status);
 
   if (status->listening_state == ListeningState::WAITING)
@@ skipping 203 matching lines @@
 PresentationDispatcher::AvailabilityStatus::AvailabilityStatus(
     const std::string& availability_url)
     : url(availability_url),
       last_known_availability(false),
       listening_state(ListeningState::INACTIVE) {}
 
 PresentationDispatcher::AvailabilityStatus::~AvailabilityStatus() {
 }
 
 }  // namespace content