Quoting the spec:
If the cascaded value of a property is the unset keyword,
then if it is an inherited property, this is treated as
inherit, and if it is not, this is treated as initial.
Spec in question:
http://dev.w3.org/csswg/css-cascade/
Also use unset in the reset-to-defaults.css we use to reset css in
reftests.
We need to store the border widths independant of them being set to 0 by
border styles, because otherwise we'd need to track that dependency and
recompute on changes, and I don't want to add more entries to
GtkCssDependencies just for this special case.
By moving the code that does the setting to 0 from the compute stage to
the query stage, we can achieve this.
Now we need to just be aware that the actual value stored is not set to
0 when we use gtk_css_computed_values_get_value().
Both _gtk_css_style_property_print_value() and
_gtk_css_style_property_compute_value() aren't necessary anymore and are
replaced by _gtk_css_value_print() and _gtk_css_value_comptue()
respectively.
Equality tests are done with _gtk_css_value_equal(). There is no need to
do it per-property, equal values will still be equal.
This essentially reverts 24f5d54329e028347bd76af42e86ed190c1229a2 and
92c7a7171e1240b6d961ee5b6f9ab6b596e98904.
The compute_value fallback path is only needed for custom properties,
the real style properties have custom compute functions if they need
them already.
For now, we return FALSE for all default css values, so this is not very
useful.
I also think of this as an optimization equal, not a guaranteed equal,
because we don't even have a notion of what "equal" means.
For example, for background-repeat, "repeat, repeat" and "repeat"
are functionally equivalent. But the cssvalue has no idea that it's used
for background-repeat.
As a more complicated example, "repeat, no-repeat" and "repeat" are
equal to what one sees as long as there's only one image listed
background-image-source. But once you start transition'ing to an image
with 2 sources, it's different...
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.
