* Electron version: 1.6.5
* Operating system: macOS Sierra

If you have a window with native tab bar to the top and you open a new window, it will open as separate window. But if you are in fullscreen mode, that new window will be attached as tab. Would it make sense to have API to force a window to open into an existing tab group or not? This would make it possible to give the user the choice of wether a window should open as tab or not independent from being in fullscreen mode or not.

Not even sure such API exists on macOS though.

/cc @tonyganch
atom/browser/native_window.cc
if (is_closed_)
    return;
  WindowList::RemoveWindow(this);
  is_closed_ = true;
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowClosed();
}
void NativeWindow::NotifyWindowEndSession() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowEndSession();
}
void NativeWindow::NotifyWindowBlur() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowBlur();
}
void NativeWindow::NotifyWindowFocus() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowFocus();
}
void NativeWindow::NotifyWindowShow() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowShow();
}
void NativeWindow::NotifyWindowHide() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowHide();
}
void NativeWindow::NotifyWindowMaximize() {