- 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
v8::Local<v8::Value> val,
                     atom::SetSizeParams* out) {
    mate::Dictionary params;
    if (!ConvertFromV8(isolate, val, &params))
      return false;
    bool autosize;
    if (params.Get("enableAutoSize", &autosize))
      out->enable_auto_size.reset(new bool(true));
    gfx::Size size;
    if (params.Get("min", &size))
      out->min_size.reset(new gfx::Size(size));
    if (params.Get("max", &size))
      out->max_size.reset(new gfx::Size(size));
    if (params.Get("normal", &size))
      out->normal_size.reset(new gfx::Size(size));
    return true;
  }
};
template<>
struct Converter<PrintSettings> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,