- 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
net::HttpResponseHeaders* headers) {
    base::DictionaryValue response_headers;
    if (headers) {
      void* iter = nullptr;
      std::string key;
      std::string value;
      while (headers->EnumerateHeaderLines(&iter, &key, &value)) {
        key = base::ToLowerASCII(key);
        if (response_headers.HasKey(key)) {
          base::ListValue* values = nullptr;
          if (response_headers.GetList(key, &values))
            values->AppendString(value);
        } else {
          scoped_ptr<base::ListValue> values(new base::ListValue());
          values->AppendString(value);
          response_headers.Set(key, std::move(values));
        }
      }
    }
    return ConvertToV8(isolate, response_headers);
  }
};
template<>
struct Converter<content::SavePageType> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,