css: Implement "unset"

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.

1 files changed, 6 insertions, 0 deletions

diff --git a/gtk/gtkcssinheritvalue.c b/gtk/gtkcssinheritvalue.c
index 053245cf73..bfea779d69 100644
--- a/gtk/gtkcssinheritvalue.c
+++ b/gtk/gtkcssinheritvalue.c
@@ -97,3 +97,9 @@ _gtk_css_inherit_value_new (void)
 {
   return _gtk_css_value_ref (&inherit);
 }
+
+GtkCssValue *
+_gtk_css_inherit_value_get (void)
+{
+  return &inherit;
+}