- 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_web_contents.cc
#include "content/public/browser/storage_partition.h"
#include "content/public/browser/site_instance.h"
#include "content/public/browser/web_contents.h"
#include "content/public/common/context_menu_params.h"
#include "native_mate/dictionary.h"
#include "native_mate/object_template_builder.h"
#include "net/http/http_response_headers.h"
#include "net/url_request/static_http_user_agent_settings.h"
#include "net/url_request/url_request_context.h"
#include "third_party/WebKit/public/web/WebInputEvent.h"
#include "ui/base/l10n/l10n_util.h"
#include "atom/common/node_includes.h"
namespace {
struct PrintSettings {
  bool silent;
  bool print_background;
};
void SetUserAgentInIO(scoped_refptr<net::URLRequestContextGetter> getter,
                      std::string accept_lang,
                      std::string user_agent) {
  getter->GetURLRequestContext()->set_http_user_agent_settings(
      new net::StaticHttpUserAgentSettings(
          net::HttpUtil::GenerateAcceptLanguageHeader(accept_lang),
          user_agent));
}
}  
namespace mate {
template<>
struct Converter<atom::SetSizeParams> {
  static bool FromV8(v8::Isolate* isolate,