Added callback to DownloadUrl() so we can find download failures.

content/browser/download/download_file_manager.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 "content/browser/download/download_file_manager.h"
 
 #include <set>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 159 matching lines @@
     }
   }
 }
 
 void DownloadFileManager::StartDownload(
     DownloadCreateInfo* info, const DownloadRequestHandle& request_handle) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(info);
 
   DownloadManager* manager = request_handle.GetDownloadManager();
-  if (!manager) {
-    request_handle.CancelRequest();
-    delete info;
-    return;
-  }
+  DCHECK(manager);  // Checked in |DownloadResourceHandler::StartOnUIThread()|.
 
   // |bound_net_log| will be used for logging the both the download item's and
   // the download file's events.
   net::BoundNetLog bound_net_log =
       manager->CreateDownloadItem(info, request_handle);
   bool hash_needed = manager->GenerateFileHash();
 
   BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
       base::Bind(&DownloadFileManager::CreateDownloadFile, this,
                  info, request_handle, make_scoped_refptr(manager),
@@ skipping 293 matching lines @@
            << " id = " << global_id
            << " download_file = " << download_file->DebugString();
 
   downloads_.erase(global_id);
 
   delete download_file;
 
   if (downloads_.empty())
     StopUpdateTimer();
 }