Created attachment 369545 [details]
Attached testcase (with layer borders on) show that we make backing that is much too big when the shared layer has a transform.
We need to do the right transform math when computing composited bounds.
We're getting localClipRect and transforming it, which seems wrong.
Created attachment 369654 [details]
Comment on attachment 369654 [details]
Clearing flags on attachment: 369654
Committed r245208: <https://trac.webkit.org/changeset/245208>
All reviewed patches have been landed. Closing bug.