Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

android_webview/renderer/aw_content_settings_client.h

 // 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.
 
 #ifndef ANDROID_WEBVIEW_RENDERER_AW_CONTENT_SETTINGS_CLIENT_H_
 #define ANDROID_WEBVIEW_RENDERER_AW_CONTENT_SETTINGS_CLIENT_H_
 
 #include "base/macros.h"
 #include "content/public/renderer/render_frame_observer.h"
 #include "third_party/WebKit/public/web/WebContentSettingsClient.h"
 
 namespace android_webview {
 
 // Android WebView implementation of blink::WebContentSettingsClient.
 class AwContentSettingsClient : public content::RenderFrameObserver,
                                 public blink::WebContentSettingsClient {
  public:
   explicit AwContentSettingsClient(content::RenderFrame* render_view);
 
  private:
   ~AwContentSettingsClient() override;
 
+  // content::RenderFrameObserver implementation.
+  void OnDestruct() override;
+
   // blink::WebContentSettingsClient implementation.
   bool allowDisplayingInsecureContent(
       bool enabled_per_settings,
       const blink::WebURL& url) override;
   bool allowRunningInsecureContent(
       bool enabled_per_settings,
       const blink::WebSecurityOrigin& origin,
       const blink::WebURL& url) override;
 
   DISALLOW_COPY_AND_ASSIGN(AwContentSettingsClient);
 };
 
 }  // namespace android_webview
 
 #endif  // ANDROID_WEBVIEW_RENDERER_AW_CONTENT_SETTINGS_CLIENT_H_