- 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
content::BrowserPpapiHost* host) {
  host->GetPpapiHost()->AddHostFactoryFilter(
      make_scoped_ptr(new chrome::ChromeBrowserPepperHostFactory(host)));
}
content::QuotaPermissionContext*
    AtomBrowserClient::CreateQuotaPermissionContext() {
  return new AtomQuotaPermissionContext;
}
void AtomBrowserClient::AllowCertificateError(
    content::WebContents* web_contents,
    int cert_error,
    const net::SSLInfo& ssl_info,
    const GURL& request_url,
    content::ResourceType resource_type,
    bool overridable,
    bool strict_enforcement,
    bool expired_previous_decision,
    const base::Callback<void(bool)>& callback,
    content::CertificateRequestResultType* request) {
  if (delegate_) {
    delegate_->AllowCertificateError(
        web_contents, cert_error, ssl_info, request_url,
        resource_type, overridable, strict_enforcement,
        expired_previous_decision, callback, request);
  }
}
void AtomBrowserClient::SelectClientCertificate(