Linux Aura: Use system title bar is now set by preference, not flag.

ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc b/ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc
index 1fdcf08be662e1233863fa866f75dd7d0c4fdda2..89ff959a42b1ba7753d7f1f166ea6e0e03bb867b 100644
--- a/ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_root_window_host_x11.cc
@@ -606,6 +606,9 @@ bool DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() const {
 }
 
 void DesktopWindowTreeHostX11::FrameTypeChanged() {
+  Widget::FrameType new_type =
+      native_widget_delegate_->AsWidget()->frame_type();
+  SetUseNativeFrame(new_type == Widget::FRAME_TYPE_FORCE_NATIVE);
   // Replace the frame and layout the contents. Even though we don't have a
   // swapable glass frame like on Windows, we still replace the frame because
   // the button assets don't update otherwise.