The mechanism allows iterating even through subresources that don't
have specific XID's. When such 'resources' are iterated, the XID for
them will be zero. A resource type can assign an iteration function
for its subresources with SetResourceTypeFindSubResFunc; by default
resources are assumed not to contain subresources.
The purpose of this extension is to enable accurate accounting of
the resources a resource consumes or uses.
This patch provides the subresource iteration functions for Windows
and GCs.
Reviewed-by: Rami Ylimäki <rami.ylimaki@vincit.fi>
Signed-off-by: Erkki Seppälä <erkki.seppala@vincit.fi>
3ba0decb4b