- 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
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) {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  bool prevent_default = Emit("certificate-error",
                              WebContents::CreateFrom(isolate(), web_contents),
                              request_url,
                              net::ErrorToString(cert_error),
                              ssl_info.cert,
                              callback);
  
  if (!prevent_default)
    *request = content::CERTIFICATE_REQUEST_RESULT_TYPE_DENY;
}
void App::SelectClientCertificate(