- 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
}
  isolate->ThrowException(v8::Exception::Error(mate::StringToV8(
      isolate, "Invalid event object")));
}
void WebContents::BeginFrameSubscription(
    const FrameSubscriber::FrameCaptureCallback& callback) {
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view) {
    scoped_ptr<FrameSubscriber> frame_subscriber(new FrameSubscriber(
        isolate(), view, callback));
    view->BeginFrameSubscription(std::move(frame_subscriber));
  }
}
void WebContents::EndFrameSubscription() {
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view)
    view->EndFrameSubscription();
}
void WebContents::OnCursorChange(const content::WebCursor& cursor) {
  content::WebCursor::CursorInfo info;
  cursor.GetCursorInfo(&info);
  if (cursor.IsCustom()) {
    Emit("cursor-changed", CursorTypeToString(info),
      gfx::Image::CreateFrom1xBitmap(info.custom_image),
      info.image_scale_factor);
  } else {
    Emit("cursor-changed", CursorTypeToString(info));
  }
}
void WebContents::SetSize(const SetSizeParams& params) {