Log Message:
Update gtk3 to 3.20.2

Many changes including:
* Fix blue background in Emacs windows
* Fix a performance issue with excessive redraws
* Active GtkSwitch widgets now use the :checked state, to match GtkToggleButton
* GTK+ now respects default size even for windows that are not resizable
* GtkScale and GtkScrollbar have received multiple fixes for fallout from
  the gadget port
* GtkStackSwitcher will now switch pages when hovered during drag-and-drop
* GtkRange, GtkScale and GtkScrollbar have been ported to use gadgets
* GTK+ will now list included backends when seeing the
  environment variable GDK_BACKEND=help
* gtk-builder-tool can now preview .ui files with custom CSS
* gtk3-demo now demonstrates saving window sizes in the application
  example, and has many more widgets in the foreign drawing example.
* GTK+ widget drawing scalability has been improved (for containers
  with many children, like large list boxes or flow boxes).
* Drag-and-Drop has been rearchitected to move the input handling into
  GDK, where different backends can handle it according to their needs
  and capabilities. The new, 'managed' DND is currently implemented
  for X11 and Wayland.

* CSS changes:
 - the rem unit is now supported
 - calc() expressions are supported, too
 - Allow loading svg imges
 - Fix baseline handling
 - -gtk-recolor() works properly with hi-dpi now
 - image() can be used in CSS now
 - Fix rendering of asymmetric borders
 - Add CSS names to more widgets
 - Support recoloring icons with -gtk-recolor
 - CSS margins, border and padding are more consistently supported
 - More widgets support min-width and min-height
 - More style properties have been superseded by CSS properties
 - Pseudo state names have been aligned with what CSS uses:
   :disabled instead of :insensitive, :indeterminate instead of
   :inconsistent and :drop(active) instead of :dnd. The old names
   still work
 - GTK+ specific CSS properties have been prefixed with -gtk-.
   The old names still work
 - The CSS syntax for Radial gradients is now supported
 - CSS documentation has been rewritten and expanded

* Inspector:
 - The per-object CSS editor has been dropped; the global one is sufficient
 - The sidebar has been replaced by a combo box
 - Add a Show Layout option to the Visual tab
 - CSS node tree and style properties are now on the same page
 - The frame clock is shown in the Miscellaneous page
 - Isolate the inspector from visual debugging effects
 - Numerous smaller UI improvements
 - Show input device information
 - Update monitor information when it changes

* Themes:
 - The HighContrast theme has been brought back up to par with Adwaita
 - Adwaita has received detail fixes for many widgets
 - Adwaita now transitions to backdrop
 - Windows theme: handle spin buttons and switches
 - Adwaita: Fixes for scales, combo boxes, info bars, action bars, radio and
   check buttons, side bars, etc
 - Adwaita has gained a new style of drop target highlighting
 - The Windows theme is now included on all platforms
 - new radio / check implementation
 - GTK+ now includes a HighContrastInverse theme which is a dark
   variant of the HighContrast theme

* Wayland:
 - Synchronize key repeat with server
 - Add a bell request to gtk_shell and use it to implement gdk_window_beep
 - Add a focus request to gtk_shell and use it to implement gtk_window_present
 - Dropping tabs to create new windows is now supported
 - Implement primary selection (using a private protocol
   with mutter for now)
 - Implement startup notification
 - Fix a significant buffer leak
 - Support kinetic scrolling, using the new events in version 5 of the
   wl_pointer interface
 - Suppport DND actions and drag cancellation that were added in version
   3 of the wl_data_offer interface

* Windows:
 - Use a custom drag-resize implementation
 - Use layered windows
 - Provide workarea information
 - The Classic and XP themes have been dropped
 - The remaining theme is being fixed to work with CSS nodes
 - React to theme changes

* Quartz:
 - Fix image retrieval from the clipboard

* OS X:
 - Native zoom and rotate gestures are now supported

For full details see:
http://git.gnome.org/browse/gtk+/tree/NEWS?h=3.20.2