no-one seems to have mentioned it, but this is apparently motivated by the aura project - http://www.chromium.org/developers/design-documents/aura-des...

you can see the link via: http://codereview.chromium.org/8680034/#ps11001 which links to bug http://code.google.com/p/chromium-os/issues/detail?id=23271 which blocks http://code.google.com/p/chromium-os/issues/detail?id=21187 which is "important to the Aura effort"