Add wxComboBox::Popup() and Dismiss() to manually show or hide its popup.

Add implementations for wxMSW and wxGTK.

Closes #11506.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63242 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/combobox.cpp

@@ -337,4 +337,13 @@ void wxComboBox::OnUpdateSelectAll(wxUpdateUIEvent& event)
     event.Enable(!wxTextEntry::IsEmpty());
 }
 
+void wxComboBox::Popup()
+{
+     gtk_combo_box_popup( GTK_COMBO_BOX(m_widget) );
+}
+
+void wxComboBox::Dismiss()
+{
+    gtk_combo_box_popdown( GTK_COMBO_BOX(m_widget) );
+}
 #endif // wxUSE_COMBOBOX