Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

android_webview/renderer/aw_message_port_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 ANDROID_WEBVIEW_RENDERER_AW_MESSAGE_PORT_CLIENT_H_
 #define ANDROID_WEBVIEW_RENDERER_AW_MESSAGE_PORT_CLIENT_H_
 
 #include <vector>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "content/public/renderer/render_frame_observer.h"
 
 namespace android_webview {
 
 // Renderer side of Android webview specific message port service. This service
 // is used to convert messages from WebSerializedScriptValue to a base value.
 class AwMessagePortClient : public content::RenderFrameObserver {
  public:
   explicit AwMessagePortClient(content::RenderFrame* render_frame);
 
  private:
   ~AwMessagePortClient() override;
 
   // RenderFrameObserver
   bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() override;
 
   void OnWebToAppMessage(int message_port_id,
                          const base::string16& message,
                          const std::vector<int>& sent_message_port_ids);
   void OnAppToWebMessage(int message_port_id,
                          const base::string16& message,
                          const std::vector<int>& sent_message_port_ids);
   void OnClosePort(int message_port_id);
 
   DISALLOW_COPY_AND_ASSIGN(AwMessagePortClient);
 };
 
 }
 
 #endif  // ANDROID_WEBVIEW_RENDERER_AW_MESSAGE_PORT_CLIENT_H_