[gtk+] (15 commits) Non-fast-forward update to branch wip/native-file-chooser

[Alexander Larsson <alexl src gnome org>]

The branch 'wip/native-file-chooser' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  455064d... TreeModelFilter: Fix uninitialized memory read.
  48575e0... Make GtkFileChooser interface require a GObject
  e4c9e3a... Add GtkNativeDialog abstract base class
  ab9392b... GtkFileFilter: Add private function to represent filter as 
  e0ad8a8... GtkFileChooserNative: Fallback and win32 implementation
  edcab8c... GtkFileChooserButton: Use native dialogs
  f036676... testgtk: Add native dialog tests

Commits added to the branch:

  c7491fa... stack: Store actual widget size, not preferred size (*)
  820a8c2... checkmenuitem: Update CSS nodes on set_active() (*)
  4247e42... stack sidebar: Remove an unused variable (*)
  7b3cda2... gtk3-demo: Drop .sidebar class (*)
  4ed47e7... Fix a crash with steppers (*)
  a6b4677... TreeModelFilter: Fix uninitialized memory read.
  db36986... Make GtkFileChooser interface require a GObject
  adc9a96... Add GtkNativeDialog abstract base class
  bedc197... GtkFileFilter: Add private function to represent filter as 
  f1f0bb2... GtkFileChooserNative: Fallback and win32 implementation
  4fbf06c... GtkFileChooserButton: Use native dialogs
  9bc8f78... testgtk: Add native dialog tests
  1bc352b... Mention native file choosers in NEWS
  eb96864... docs: Move GtkNativeDialog section to "abstract base classe
  ca2042e... gtk3-demo: Add open file to the application demo

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