- 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
}
void WebContents::RenderViewDeleted(content::RenderViewHost* render_view_host) {
  Emit("render-view-deleted", render_view_host->GetProcess()->GetID());
}
void WebContents::RenderProcessGone(base::TerminationStatus status) {
  Emit("crashed");
}
void WebContents::PluginCrashed(const base::FilePath& plugin_path,
                                base::ProcessId plugin_pid) {
  content::WebPluginInfo info;
  auto plugin_service = content::PluginService::GetInstance();
  plugin_service->GetPluginInfoByPath(plugin_path, &info);
  Emit("plugin-crashed", info.name, info.version);
}
void WebContents::MediaStartedPlaying(const MediaPlayerId& id) {
  Emit("media-started-playing");
}
void WebContents::MediaStoppedPlaying(const MediaPlayerId& id) {
  Emit("media-paused");
}
void WebContents::DidChangeThemeColor(SkColor theme_color) {
  std::string hex_theme_color = base::StringPrintf("#%02X%02X%02X",
    SkColorGetR(theme_color),
    SkColorGetG(theme_color),
    SkColorGetB(theme_color));
  Emit("did-change-theme-color", hex_theme_color);
}
void WebContents::DocumentLoadedInFrame(