No need to pass DownloadItemModel ownership.

chrome/browser/download/download_item_model.cc

 // Copyright (c) 2012 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_item_model.h"
 
 #include "base/i18n/number_formatting.h"
 #include "base/i18n/rtl.h"
 #include "base/string16.h"
 #include "base/supports_user_data.h"
@@ skipping 200 matching lines @@
 // -----------------------------------------------------------------------------
 // DownloadItemModel
 
 DownloadItemModel::DownloadItemModel(DownloadItem* download)
     : download_(download) {
 }
 
 DownloadItemModel::~DownloadItemModel() {
 }
 
-void DownloadItemModel::CancelTask() {
-  download_->Cancel(true /* update history service */);
-}
-
 string16 DownloadItemModel::GetInterruptReasonText() const {
   if (download_->GetState() != DownloadItem::INTERRUPTED ||
       download_->GetLastReason() ==
       content::DOWNLOAD_INTERRUPT_REASON_USER_CANCELED) {
     return string16();
   }
   return InterruptReasonMessage(download_->GetLastReason());
 }
 
 string16 DownloadItemModel::GetStatusText() const {
@@ skipping 214 matching lines @@
   }
 
   // In progress download with no known time left and non-zero completed bytes:
   // "100/120 MB" or "100 MB"
   if (GetCompletedBytes() > 0)
     return size_ratio;
 
   // Instead of displaying "0 B" we say "Starting..."
   return l10n_util::GetStringUTF16(IDS_DOWNLOAD_STATUS_STARTING);
 }