- 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
if (FAILED(hr)) {
    ui::win::OpenFolderViaShell(dir);
    return;
  }
  const ITEMIDLIST* highlight[] = {file_item};
  hr = SHOpenFolderAndSelectItems(dir_item, base::size(highlight), highlight,
                                  NULL);
  if (FAILED(hr)) {
    
    
    
    if (hr == ERROR_FILE_NOT_FOUND) {
      ShellExecute(NULL, L"open", dir.value().c_str(), NULL, NULL, SW_SHOW);
    } else {
      LOG(WARNING) << " " << __func__ << "(): Can't open full_path = \""
                   << full_path.value() << "\""
                   << " hr = " << logging::SystemErrorCodeToString(hr);
      ui::win::OpenFolderViaShell(dir);
    }
  }
}
}  
namespace platform_util {
void ShowItemInFolder(const base::FilePath& full_path) {
  base::CreateCOMSTATaskRunner(
      {base::ThreadPool(), base::MayBlock(), base::TaskPriority::USER_BLOCKING})
      ->PostTask(FROM_HERE,
                 base::BindOnce(&ShowItemInFolderOnWorkerThread, full_path));
}
bool OpenItem(const base::FilePath& full_path) {