- Electron version: 1.3.6
- Operating system: Windows 7 x64
- Other: Microsoft Office 2013 (will make more sense in a bit)

`shell.openItem()` is a blocking call, it would be nice if it's async or has an async version to handle synchronous external application behavior.

Reproduce: 
Open a password-protected Microsoft Excel file, `shell.openItem()` will be blocking until the Password window is submitted or dismissed. Consequently Microsoft Word does not have this issue.

Related to #2761.

shell/common/platform_util_win.cc
return S_OK;
}
HRESULT DeleteFileProgressSink::PostRenameItem(DWORD,
                                               IShellItem*,
                                               __RPC__in_string LPCWSTR,
                                               HRESULT,
                                               IShellItem*) {
  return E_NOTIMPL;
}
HRESULT DeleteFileProgressSink::PreMoveItem(DWORD,
                                            IShellItem*,
                                            IShellItem*,
                                            LPCWSTR) {
  return E_NOTIMPL;
}
HRESULT DeleteFileProgressSink::PostMoveItem(DWORD,
                                             IShellItem*,
                                             IShellItem*,
                                             LPCWSTR,
                                             HRESULT,
                                             IShellItem*) {
  return E_NOTIMPL;
}
HRESULT DeleteFileProgressSink::PreCopyItem(DWORD,
                                            IShellItem*,
                                            IShellItem*,
                                            LPCWSTR) {
  return E_NOTIMPL;
}
HRESULT DeleteFileProgressSink::PostCopyItem(DWORD,