Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/public/renderer/render_frame_observer.cc

 // 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.
 
 #include "content/public/renderer/render_frame_observer.h"
 
 #include "content/renderer/render_frame_impl.h"
 
 using blink::WebFrame;
 
@@ skipping 11 matching lines @@
   }
 }
 
 RenderFrameObserver::~RenderFrameObserver() {
   if (render_frame_) {
     RenderFrameImpl* impl = static_cast<RenderFrameImpl*>(render_frame_);
     impl->RemoveObserver(this);
   }
 }
 
-void RenderFrameObserver::OnDestruct() {
-  delete this;
-}
-
 bool RenderFrameObserver::OnMessageReceived(const IPC::Message& message) {
   return false;
 }
 
 bool RenderFrameObserver::Send(IPC::Message* message) {
   if (render_frame_)
     return render_frame_->Send(message);
 
   delete message;
   return false;
 }
 
 RenderFrame* RenderFrameObserver::render_frame() const {
   return render_frame_;
 }
 
 void RenderFrameObserver::RenderFrameGone() {
   render_frame_ = NULL;
 }
 
 }  // namespace content