- 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_session.cc
#include "atom/browser/api/atom_api_session.h"
#include <map>
#include <string>
#include <vector>
#include "atom/browser/api/atom_api_cookies.h"
#include "atom/browser/api/atom_api_download_item.h"
#include "atom/browser/api/atom_api_protocol.h"
#include "atom/browser/api/atom_api_web_request.h"
#include "atom/browser/atom_browser_context.h"
#include "atom/browser/atom_browser_main_parts.h"
#include "atom/browser/atom_permission_manager.h"
#include "atom/browser/browser.h"
#include "atom/browser/net/atom_cert_verifier.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/native_mate_converters/content_converter.h"
#include "atom/common/native_mate_converters/file_path_converter.h"
#include "atom/common/native_mate_converters/gurl_converter.h"
#include "atom/common/native_mate_converters/net_converter.h"
#include "atom/common/native_mate_converters/value_converter.h"
#include "atom/common/node_includes.h"
#include "base/files/file_path.h"
#include "base/guid.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"