It was introduced by bug 111724. We can get rid of it by passing the world type explicitly to the HasInstance functions.
Created attachment 192763 [details] Patch
Comment on attachment 192763 [details] Patch Attachment 192763 [details] did not pass cr-linux-debug-ews (chromium-xvfb): Output: http://webkit-commit-queue.appspot.com/results/17138123
Comment on attachment 192763 [details] Patch Looks reasonable. Please fix the debug build failure before landing. (I was wondering why you had to introduce GetFromContext in the previous patch:-)
There are some newly discovered problems which prevent doing this, see bug 112250.
This is no longer needed, the new patch in bug 111724 no longer introduces this GetFromContext world type.