Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

components/nacl/renderer/nacl_helper.cc

 // Copyright 2014 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/nacl/renderer/nacl_helper.h"
 
 #include "content/public/renderer/renderer_ppapi_host.h"
 
 namespace nacl {
 
 NaClHelper::NaClHelper(content::RenderFrame* render_frame)
     : RenderFrameObserver(render_frame) {}
 
 NaClHelper::~NaClHelper() {}
 
 void NaClHelper::DidCreatePepperPlugin(content::RendererPpapiHost* host) {
   // The Native Client plugin is a host for external plugins.
   if (host->GetPluginName() == "Native Client")
     host->SetToExternalPluginHost();
 }
 
+void NaClHelper::OnDestruct() {
+  delete this;
+}
+
 }  // namespace nacl