- Electron version: 1.4.3
- Operating system:  @win7
- description:

working on a download app with electron and angular. 
By using webContents.downloadUrl, webContents.session.on('will-download', handler) I can make download function work well, however, I could not find a api to save download progress before closing electron app so that I can restore download when this app is started next time.

Excepted Result:
1. user click 'download' button to download a 1G file.
2. after 500M is downloaded, user quit the app
3. one hour later, user open this app again, and downloading can automatically be restored

atom/browser/api/atom_api_download_item.h
#ifndef ATOM_BROWSER_API_ATOM_API_DOWNLOAD_ITEM_H_
#define ATOM_BROWSER_API_ATOM_API_DOWNLOAD_ITEM_H_
#include <string>
#include "atom/browser/api/trackable_object.h"
#include "base/files/file_path.h"
#include "content/public/browser/download_item.h"
#include "native_mate/handle.h"
#include "url/gurl.h"
namespace atom {
namespace api {
class DownloadItem : public mate::TrackableObject<DownloadItem>,
                     public content::DownloadItem::Observer {
 public:
  static mate::Handle<DownloadItem> Create(v8::Isolate* isolate,
                                           content::DownloadItem* item);
  static void BuildPrototype(v8::Isolate* isolate,
                             v8::Local<v8::FunctionTemplate> prototype);
  void Pause();