Log Message:
Update gtk3 to 3.12.2

Highlights from changes:

* GtkPopover: A new widget that is can be used for transient
  views, as an alternative to menus or dialogs.
 - GtkMenuButton can use popovers instead of menus
* Client-side decorations:
 - Make F10 move focus to the header bar
 - Make header bars draggable on touch systems
 - Make shadows unclickable
* Printing: Google cloud print support
* GtkActionBar is a new widget that is meant to be used
  for actions at the bottom of a window.
* GtkAppChooserDialog has been redesigned

* GtkBox can now place a widget centered, regardless of
  the sizes of children on either side, similar to GtkHeaderBar.
* Dialogs:
 - Dialogs have been modernized, can use a header bar now
 - Built-in dialogs react to a setting, gtk-dialogs-use-header
   for this, dialogs derived from GtkDialog: default to no headerbar
 - GtkAssistant also respects the setting
* OS X:
 - Better menu integration. Items such as 'Hide', 'Hide Others'
   and 'Show All' are now handled specially
 - GTK+ provides a default application menu now
* Theming:
 - GTK+ now uses RGBA visuals by default
 - Notebook tabs now support a prelight state
 - Reorderable notebook tabs can be themed differently
* GtkActionBar: A new container, which has a centered
  child like GtkHeaderBar. It can be used in places
  where header bar theming is not suitable
* GtkAppChooser: The online support has been simplified
  and modernized
* GtkHeaderBar button theming has been changed to be
  more flexible. There is now a gtk-decoraton-layout
  setting and a decoration-layout property.
* Accessibility:
  - Links in labels are now accessible
  - Model-based menus are accessible
  - Accessible roles of several widgets have been fixed
  - GtkColorChooser accessibility is improved
* Theming: The Raleigh theme has been updated for
  several new features, including client-side decorations
* Model-based menus now support a hidden-when attribute
  on items that allows them to be hidden on various
  conditions
* New notebook tab styling: GtkNotebook now offers a way
  for themes to opt out of the tab rendering, with the
  'has-tab-gap' style property. The Adwaita theme is using
  this to achieve a more modern tab appearance.
* GtkFlowBox: A container that its children in a reflowing
  grid, which can be oriented horizontally or vertically.
  It is similar to GtkListBox in that the children can
  be sorted and filtered, and by requiring a dedicated child
  widget type, GtkFlowBoxChild. It is similar to GtkTreeView
  in that is supports a full set of selection modes, including
  rubberband selection.
* GtkStack: children can now indicate that they require
  attention by setting the needs-attention child property.
* Broadway now requires binary array buffers and modern WebSocket
  protocol support
* Autoscrolling in range widgets has been improved to work more
  reliably in maximized windows.
* GtkSpinner has been changed to render in in a limited set of
  sizes.
* GtkApplication now stores and handles accelerators for GActions
  itself.
* GtkIconTheme now falls back to the gnome icontheme to fix
  problems with the availability of symbolic icons in other
  icon themes.
* GTK+ respects the deprecated gtk-button-images and gtk-menu-images
  settings again.

For full details see:
https://git.gnome.org/browse/gtk+/tree/NEWS?id=3.12.2