- 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
const content::WebContents* web_contents) {
  auto context = web_contents->GetBrowserContext();
  auto site_instance = web_contents->GetSiteInstance();
  if (!context || !site_instance)
    return nullptr;
  auto storage_partition =
      content::BrowserContext::GetStoragePartition(context, site_instance);
  if (!storage_partition)
    return nullptr;
  return storage_partition->GetServiceWorkerContext();
}
}  
WebContents::WebContents(content::WebContents* web_contents)
    : content::WebContentsObserver(web_contents),
      type_(REMOTE) {
  AttachAsUserData(web_contents);
  web_contents->SetUserAgentOverride(GetBrowserContext()->GetUserAgent());
}
WebContents::WebContents(v8::Isolate* isolate,