Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/idle_user_detector.cc

 // Copyright (c) 2011 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/idle_user_detector.h"
 
 #include "base/logging.h"
 #include "content/common/input_messages.h"
 #include "content/public/renderer/content_renderer_client.h"
 #include "content/renderer/render_thread_impl.h"
@@ skipping 19 matching lines @@
     const ui::LatencyInfo& latency_info,
     InputEventDispatchType dispatch_type) {
   if (GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden()) {
     RenderThreadImpl* render_thread = RenderThreadImpl::current();
     if (render_thread != NULL) {
       render_thread->PostponeIdleNotification();
     }
   }
 }
 
+void IdleUserDetector::OnDestruct() {
+  delete this;
+}
+
 }  // namespace content