We've seen Deadlock caused by PluginViewPrivate::destroyBuffers locking mutexex ans sending sync message at the same time.
Created attachment 179798 [details] the patch (shrink the mutex locking scope)
Comment on attachment 179798 [details] the patch (shrink the mutex locking scope) LGTM.
Created attachment 179802 [details] updated to commit
Comment on attachment 179802 [details] updated to commit Clearing flags on attachment: 179802 Committed r137949: <http://trac.webkit.org/changeset/137949>
All reviewed patches have been landed. Closing bug.