[gtk/matthiasc/for-master] (15 commits) ...stackswitcher: Drop the Private struct

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  56565b1... reftests: Fix the window-show-contents-on-map test (*)
  fa2a8ac... reftests: Remove window-show-contents-on-map from xfails (*)
  a8e04ee... Merge branch 'matthiasc/for-master' into 'master' (*)
  7874b29... Adwaita: remove margin from GtkWindowControls when empty (*)
  764e43b... Merge branch 'wip/exalm/windowcontrols-fix' into 'master' (*)
  0b6cd34... Merge branch 'matthiasc/for-master' into 'master' (*)
  9156be6... viewport: Drop the Private struct
  2ea7f47... separator: Drop the Private struct
  7ede3b9... calendar: Drop the Private struct
  a78e0f1... fontchooserwidget: Drop the Private struct
  5bd2b49... fontchooserdialog: Drop the Private struct
  bf77694... linkbutton: Drop the Private struct
  2356c9b... overlay: Drop the Private struct
  508ed21... progressbar: Drop the Private struct
  dc99a7a... stackswitcher: Drop the Private struct

(*) This commit already existed in another branch; no separate mail sent