The parent refs the child, so gtk_css_node_set_parent() adds/removes a
reference.
We should probably refactor this so that we name the function
parent.add(node) instead of node.set_parent(parent) - makes the
refcounting more clear.
- GtkCssWidgetNode
for style contexts owned by a widget
- GtkCssPathNode
for style contexts using a GtkWidgetPath
- GtkCssTransientNode
for nodes created with gtk_style_context_save()/restore()
The functionality of it is supposed to grow, so better put it in a
custom file early.
This is just a naive split so far, the next patches will split things
further.
