We now store the symbolic colors as a GtkCssValue which means that
we can reuse the color when resolving and storing the color in
the computed values in the style context.
Additionally we keep a last_resolved GtkCssValue cache in the
GtkSymbolicColor, and if resolving the color returns the same as
last time we reuse the old value. This further increases sharing
of Css Values.
Also, in places where we're computing a new CssValue based on an
old one, make sure that if nothing changes we're returning a reference
to the old one, rather than creating a new identical instance.
Instead of on-demand resolvage, we now resolve during lookup. The step
is done via
_gtk_css_style_property_compute_value()
which currently calls into
_gtk_css_style_compute_value()
That function has all the old resolving machinery.
The only part missing for now is the handling of win32 code. It will be
added back later.
