This upstreams http://code.google.com/p/chromium/issues/detail?id=154545 You can find such Region related APIs by searching [Conditional=CSS_REGIONS] through IDL files.
Created attachment 168174 [details] WIP
A related bug, filed on a similar issue: https://bugs.webkit.org/show_bug.cgi?id=94070
*** This bug has been marked as a duplicate of bug 94070 ***