Fix DownloadPermissionRequest crash when host_ disappears

chrome/browser/download/download_permission_request.cc

 // Copyright 2014 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 "chrome/browser/download/download_permission_request.h"
 
 #include "chrome/grit/generated_resources.h"
 #include "content/public/browser/web_contents.h"
 #include "grit/theme_resources.h"
 #include "ui/base/l10n/l10n_util.h"
 
 DownloadPermissionRequest::DownloadPermissionRequest(
     base::WeakPtr<DownloadRequestLimiter::TabDownloadState> host)
-    : host_(host) {}
+    : host_(host) {
+  const content::WebContents* web_contents = host_->web_contents();
+  DCHECK(web_contents);
+  request_url_ = web_contents->GetURL();
+}
 
 DownloadPermissionRequest::~DownloadPermissionRequest() {}
 
 int DownloadPermissionRequest::GetIconID() const {
   return IDR_INFOBAR_MULTIPLE_DOWNLOADS;
 }
 
 base::string16 DownloadPermissionRequest::GetMessageText() const {
   return l10n_util::GetStringUTF16(IDS_MULTI_DOWNLOAD_WARNING);
 }
 
 base::string16 DownloadPermissionRequest::GetMessageTextFragment() const {
   return l10n_util::GetStringUTF16(IDS_MULTI_DOWNLOAD_PERMISSION_FRAGMENT);
 }
 
 bool DownloadPermissionRequest::HasUserGesture() const {
   // TODO(felt): Right now, the user gesture is not being used so this value
   // does not matter. The user gesture-related code either needs to be
   // deprecated, or clients (like DownloadPermissionRequest) with their own
   // user intent policies need to be able to disable/control the bubble request
   // visibility & coalescing logic. See crbug.com/446607.
   return false;
 }
 
 GURL DownloadPermissionRequest::GetRequestingHostname() const {
-  const content::WebContents* web_contents = host_->web_contents();
-  if (web_contents) {
-    return web_contents->GetURL();
-  }
-  return GURL();
+  return request_url_;
 }
 
 void DownloadPermissionRequest::PermissionGranted() {
   if (host_) {
     // This may invalidate |host_|.
     host_->Accept();
   }
 }
 
 void DownloadPermissionRequest::PermissionDenied() {
   if (host_) {
     // This may invalidate |host_|.
     host_->Cancel();
   }
 }
 
 void DownloadPermissionRequest::Cancelled() {
   // TODO(gbillock): There's currently no suitable method for telling the host
   // that a request is cancelled.
 }
 
 void DownloadPermissionRequest::RequestFinished() {
   delete this;
 }