Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/banners/app_banner_client.h

 // 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.
 
 #ifndef CHROME_RENDERER_BANNERS_APP_BANNER_CLIENT_H_
 #define CHROME_RENDERER_BANNERS_APP_BANNER_CLIENT_H_
 
 #include <stdint.h>
 #include <string>
 
 #include "base/id_map.h"
 #include "base/macros.h"
 #include "content/public/renderer/render_frame_observer.h"
 #include "third_party/WebKit/public/platform/modules/app_banner/WebAppBannerClient.h"
 #include "third_party/WebKit/public/platform/modules/app_banner/WebAppBannerPromptResult.h"
 
 namespace IPC {
 class Message;
 }  // namespace IPC
 
 class AppBannerClient : public content::RenderFrameObserver,
                         public blink::WebAppBannerClient {
  public:
   explicit AppBannerClient(content::RenderFrame* render_frame);
   ~AppBannerClient() override;
 
  private:
-  // content::RenderFrame::Observer implementation.
+  // content::RenderFrameObserver implementation.
   void OnDestruct() override;
-
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // WebAppBannerClient implementation.
   void registerBannerCallbacks(int request_id,
                                blink::WebAppBannerCallbacks*) override;
 
   void showAppBanner(int request_id) override;
 
   void ResolveEvent(int request_id,
                     const std::string& platform,
                     const blink::WebAppBannerPromptResult::Outcome& outcome);
   void OnBannerAccepted(int request_id, const std::string& platform);
   void OnBannerDismissed(int request_id);
 
   IDMap<blink::WebAppBannerCallbacks, IDMapOwnPointer>
       banner_callbacks_;
 
   DISALLOW_COPY_AND_ASSIGN(AppBannerClient);
 };
 
 #endif  // CHROME_RENDERER_BANNERS_APP_BANNER_CLIENT_H_