- 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/atom_browser_client.cc
return l10n_util::GetApplicationLocale("");
}
void AtomBrowserClient::OverrideSiteInstanceForNavigation(
    content::BrowserContext* browser_context,
    content::SiteInstance* current_instance,
    const GURL& url,
    content::SiteInstance** new_instance) {
  if (g_suppress_renderer_process_restart) {
    g_suppress_renderer_process_restart = false;
    return;
  }
  
  if (url.SchemeIs(url::kJavaScriptScheme))
    return;
  *new_instance = content::SiteInstance::CreateForURL(browser_context, url);
  
  auto current_process = current_instance->GetProcess();
  auto pending_process = (*new_instance)->GetProcess();
  pending_processes_[pending_process->GetID()] = current_process->GetID();
  
  current_process->AddObserver(this);
}
void AtomBrowserClient::AppendExtraCommandLineSwitches(
    base::CommandLine* command_line,
    int process_id) {
  std::string process_type = command_line->GetSwitchValueASCII("type");
  if (process_type != "renderer")