Shadow and padding was never part of theme. This format was created by
mutter, and it is an incompatible change.

It's useful to get frame shapes and manipulate them within Mutter, for
example so that the compositor can use them to clip drawing.
For this, we'll need the regions as cairo regions not X regions, so
convert frame shaping code to work in terms of cairo_region_t.

https://bugzilla.gnome.org/show_bug.cgi?id=635268

This adds 'invisible_border' to metacity theme. This invisible
border will be used for resize cursor area.

Add app-menu button support in themes. This is done only to support
metacity theme format 3.5 version. Marco will not show this
button!

Based on metacity commit:
https://gitlab.gnome.org/GNOME/metacity/commit/6a2cc159

https://bugzilla.gnome.org/show_bug.cgi?id=662962

* Fix missing white border on outline window.
* Do not create outline_window if we are not going to use it.

Adapted from https://gitlab.gnome.org/GNOME/metacity/commit/a7dd0727

gtk:custom() requires a fallback color in case the GTK+ theme in use
does not define the desired color. As in general the fallback color
will approximate the intended color, there is the risk of typos going
unnoticed. To make catching these kind of errors easier, allow to ignore
the fallback color specified (and fall back to a nice shade of pink
instead) by setting an environment variable.

https://bugzilla.gnome.org/show_bug.cgi?id=656112

Add an additional color type to pick up colors defined with
@define-color in the GTK+ theme's CSS:

  gtk:custom(name,fallback)

(where "name" refers to the name defined in GTK+'s CSS, and fallback
refers to an alternative color spec which is used when the color
referenced by "name" is not found)

The main intent of the change is to allow designers to improve
Adwaita's dark theme variant without having to compromise on colors
which work in the light variant as well.

https://bugzilla.gnome.org/show_bug.cgi?id=648709

NOTE: Patch copied from mutter and adapted for metacity.

With the existing background functions, single buttons can not be
styled separately - on the left side, the style of the left button
is picked, and the right button's style on the right side.

As theme authors may want to add rounded corners to button groups
as a whole, it makes sense to treat the case of a single button in
a group differently.

https://bugzilla.gnome.org/show_bug.cgi?id=635683

NOTE: Patch copied from mutter and adapted for metacity.