- Electron version: v0.37.5
- Operating system: Any

It would be useful if we can open DevTools choosing all of it's available position: detached, docked right or docked bottom.

The new API could be something like this:
# webContents.openDevTools([options])

Opens the devtools.
- options Object (optional)
  - mode String - ['detached' | 'right' | 'bottom'] . opens DevTools in specified position. Defaults to last used mode.
  - detach Boolean - opens DevTools in a new window (deprecated, use mode: 'detached')

atom/browser/api/atom_api_web_contents.cc
return web_contents()->GetUserAgentOverride();
}
void WebContents::InsertCSS(const std::string& css) {
  web_contents()->InsertCSS(css);
}
bool WebContents::SavePage(const base::FilePath& full_file_path,
                           const content::SavePageType& save_type,
                           const SavePageHandler::SavePageCallback& callback) {
  auto handler = new SavePageHandler(web_contents(), callback);
  return handler->Handle(full_file_path, save_type);
}
void WebContents::OpenDevTools(mate::Arguments* args) {
  if (type_ == REMOTE)
    return;
  bool detach = false;
  if (type_ == WEB_VIEW) {
    detach = true;
  } else if (args && args->Length() == 1) {
    mate::Dictionary options;
    args->GetNext(&options) && options.Get("detach", &detach);
  }
  managed_web_contents()->SetCanDock(!detach);
  managed_web_contents()->ShowDevTools();
}
void WebContents::CloseDevTools() {