Make synchronized_configure work for child windows (used by in-process plugs) and ensures a native window exist
Make synchronized_configure work for child windows (used by in-process plugs) and ensures a native window exist

jessevdk/gtk,bratsche/gtk-,grubersjoe/adwaita,alexlarsson/gtk,ahodesuka/gtk,Adamovskiy/gtk,davidgumberg/gtk,zsx/gtk,Adamovskiy/gtk,davidgumberg/gtk,jessevdk/gtk,simokivimaki/gtk,davidt/gtk,chergert/gtk,Unity-Technologies/gtk,ebassi/gtk,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,Distrotech/gtk2,Lyude/gtk-,msteinert/gtk,Distrotech/gtk,zsx/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,Adamovskiy/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,simokivimaki/gtk,Adamovskiy/gtk,msteinert/gtk,zsx/gtk,Lyude/gtk-,jessevdk/gtk,chipx86/gtk,davidt/gtk,jadahl/gtk,jessevdk/gtk,Distrotech/gtk2,chipx86/gtk,chipx86/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,jigpu/gtk,grubersjoe/adwaita,chipx86/gtk,davidgumberg/gtk,Lyude/gtk-,ahodesuka/gtk,bratsche/gtk-,ahodesuka/gtk,jadahl/gtk,davidgumberg/gtk,ebassi/gtk,ebassi/gtk,jessevdk/gtk,johne53/MB3Gtk-2,chergert/gtk,davidt/gtk,chergert/gtk,alexlarsson/gtk,ahodesuka/gtk,alexlarsson/gtk,Unity-Technologies/gtk,msteinert/gtk,jessevdk/gtk,ebassi/gtk,nacho/gtk-,davidgumberg/gtk,Adamovskiy/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,jadahl/gtk,alexlarsson/gtk,johne53/MB3Gtk-2,davidgumberg/gtk,davidgumberg/gtk,Distrotech/gtk,alexlarsson/gtk,jigpu/gtk,jessevdk/gtk,Lyude/gtk-,johne53/MB3Gtk-2,Lyude/gtk-,bratsche/gtk-,ahodesuka/gtk,msteinert/gtk,chipx86/gtk,zsx/gtk,grubersjoe/adwaita,ebassi/gtk,Unity-Technologies/gtk,Distrotech/gtk2,grubersjoe/adwaita,davidgumberg/gtk,Adamovskiy/gtk,chergert/gtk,jigpu/gtk,bratsche/gtk-,ahodesuka/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,Distrotech/gtk,chergert/gtk,Distrotech/gtk2,Adamovskiy/gtk,nacho/gtk-,jadahl/gtk,grubersjoe/adwaita,nacho/gtk-,johne53/MB3Gtk-2,zsx/gtk,simokivimaki/gtk,grubersjoe/adwaita,Adamovskiy/gtk,Sidnioulz/SandboxGtk,simokivimaki/gtk,jadahl/gtk,msteinert/gtk,Distrotech/gtk,Lyude/gtk-,jadahl/gtk,bratsche/gtk-,davidt/gtk,chergert/gtk,Distrotech/gtk2,Distrotech/gtk,johne53/MB3Gtk-2,davidt/gtk,simokivimaki/gtk,jadahl/gtk,Unity-Technologies/gtk,msteinert/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,nacho/gtk-,Lyude/gtk-,Distrotech/gtk2,chergert/gtk,alexlarsson/gtk,bratsche/gtk-,simokivimaki/gtk,davidt/gtk,grubersjoe/adwaita,nacho/gtk-,ebassi/gtk,Unity-Technologies/gtk