- Electron version: v0.36.9
- Operating system: Windows 10/OS X

In #779 a `disposition` was added to the `new-window` event in [webContents](https://github.com/atom/electron/blob/master/docs/api/web-contents.md#event-new-window) but it always seems to be set to `new-window` when clicking on target="_blank" links in our web app wrapper: https://github.com/irccloud/irccloud-desktop/blob/v0.1.3/app/main.js#L109

If I Ctrl (Win) or Cmd (OS X) or middle click on links, I would expect to see a `background-tab` disposition, as in Chrome that will open links in a background tab, while keeping focus on the current tab. I'd like to catch this behaviour to set `activate` to false in `shell.openExternal`.

Is this possible?

atom/browser/api/atom_api_app.cc
const ProcessSingleton::NotificationCallback& callback) {
  if (process_singleton_.get())
    return false;
  base::FilePath user_dir;
  PathService::Get(brightray::DIR_USER_DATA, &user_dir);
  process_singleton_.reset(new ProcessSingleton(
      user_dir, base::Bind(NotificationCallbackWrapper, callback)));
  switch (process_singleton_->NotifyOtherProcessOrCreate()) {
    case ProcessSingleton::NotifyResult::LOCK_ERROR:
    case ProcessSingleton::NotifyResult::PROFILE_IN_USE:
    case ProcessSingleton::NotifyResult::PROCESS_NOTIFIED:
      process_singleton_.reset();
      return true;
    case ProcessSingleton::NotifyResult::PROCESS_NONE:
    default:  
      return false;
  }
}
mate::ObjectTemplateBuilder App::GetObjectTemplateBuilder(
    v8::Isolate* isolate) {
  auto browser = base::Unretained(Browser::Get());
  return mate::ObjectTemplateBuilder(isolate)
      .SetMethod("quit", base::Bind(&Browser::Quit, browser))
      .SetMethod("exit", base::Bind(&Browser::Exit, browser))
      .SetMethod("focus", base::Bind(&Browser::Focus, browser))
      .SetMethod("getVersion", base::Bind(&Browser::GetVersion, browser))
      .SetMethod("setVersion", base::Bind(&Browser::SetVersion, browser))
      .SetMethod("getName", base::Bind(&Browser::GetName, browser))
      .SetMethod("setName", base::Bind(&Browser::SetName, browser))
      .SetMethod("isReady", base::Bind(&Browser::is_ready, browser))