Fix two URLRequestJob subclasses that didn't support cancellation

components/about_handler/url_request_about_job.h

 // 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.
 
 #ifndef COMPONENTS_ABOUT_HANDLER_URL_REQUEST_ABOUT_JOB_H_
 #define COMPONENTS_ABOUT_HANDLER_URL_REQUEST_ABOUT_JOB_H_
 
 #include <string>
 
 #include "base/memory/weak_ptr.h"
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_job.h"
 
 namespace about_handler {
 
 class URLRequestAboutJob : public net::URLRequestJob {
  public:
   URLRequestAboutJob(net::URLRequest* request,
                      net::NetworkDelegate* network_delegate);
 
   // URLRequestJob:
   void Start() override;
+  void Kill() override;
   bool GetMimeType(std::string* mime_type) const override;
 
  private:
   ~URLRequestAboutJob() override;
 
   void StartAsync();
 
   base::WeakPtrFactory<URLRequestAboutJob> weak_factory_;
 };
 
 }  // namespace about_handler
 
 #endif  // COMPONENTS_ABOUT_HANDLER_URL_REQUEST_ABOUT_JOB_H_