* **Electron Version:**
  4.0.2
* **Operating System:**
  macOS 10.14.3
* **Last Known Working Electron version:**:
  1.7

### Expected Behavior
When creating a BrowserWindow it should not appear in the dock menu by defaults.

### Actual Behavior
It appears in the dock menu (example: `raven` in https://electronjs.org/docs/tutorial/macos-dock)

### To Reproduce
Just create new BrowserWindow, then right click on the app icon in the dock. (see https://electronjs.org/docs/tutorial/macos-dock)

At least it should be a way to control that, this can be achieve for top level window with:
`[window_ setExcludedFromWindowsMenu:YES];`, indeed [window isExcludedFromWindowsMenu] returns false by default, see

https://developer.apple.com/documentation/appkit/nsapplication/1428625-removewindowsitem
`Use the isExcludedFromWindowsMenu method of NSWindow if you want the item to remain excluded from the Window menu.`
https://developer.apple.com/documentation/appkit/nswindow/1419175-isexcludedfromwindowsmenu

atom/browser/native_window_views.cc
if (content_view()) {
    root_view_->RemoveChildView(content_view());
  }
  set_content_view(view);
  focused_view_ = view;
  root_view_->AddChildView(content_view());
  root_view_->Layout();
}
void NativeWindowViews::Close() {
  if (!IsClosable()) {
    WindowList::WindowCloseCancelled(this);
    return;
  }
  widget()->Close();
}
void NativeWindowViews::CloseImmediately() {
  widget()->CloseNow();
}
void NativeWindowViews::Focus(bool focus) {
  
  if (!IsVisible())
    return;
  if (focus) {
    widget()->Activate();
  } else {
    widget()->Deactivate();
  }
}
bool NativeWindowViews::IsFocused() {