Supplementable and Supplement instances should only be used in the thread that created them. Adding an assertion to help detect when someone is unknowingly violating this design premise.
Created attachment 184282 [details]
Comment on attachment 184282 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=184282&action=review
> + ThreadIdentifier m_threadId;
I wonder if this is the right thing for code that uses libdispatch. I think there's some other notion of thread affinity that we're supposed to use in those cases.
Landed in r140580: <http://trac.webkit.org/changeset/140580>