Currently, the shared unit use counter is updated overtime startProducingData/stopProducingData is called.
Created attachment 309360 [details] Patch
<rdar://problem/32051782>
Comment on attachment 309360 [details] Patch Clearing flags on attachment: 309360 Committed r216432: <http://trac.webkit.org/changeset/216432>
All reviewed patches have been landed. Closing bug.