Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/shell/renderer/shell_render_view_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/shell/renderer/shell_render_view_observer.h"
 
 #include "base/command_line.h"
 #include "content/public/renderer/render_view.h"
 #include "content/public/renderer/render_view_observer.h"
 #include "content/shell/common/shell_switches.h"
@@ skipping 10 matching lines @@
 }
 
 void ShellRenderViewObserver::DidClearWindowObject(
     blink::WebLocalFrame* frame) {
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kExposeInternalsForTesting)) {
     blink::WebTestingSupport::injectInternalsObject(frame);
   }
 }
 
+void ShellRenderViewObserver::OnDestruct() {
+  delete this;
+}
+
 }  // namespace content