In CanvasRenderingContext2DBase, instead of downcasting the CanvasBase object to HTMLCanvasElement, call CanvasBase methods introduced in bug #182503, making it possible for OffscreenCanvas to leverage this class properly.
Created attachment 333582 [details] WIP patch Depends on changes in bug #182503.
Created attachment 334802 [details] Patch Reviewable, but still depends on bug #182503.
Created attachment 379890 [details] Patch
Created attachment 380621 [details] Patch
Created attachment 381184 [details] Patch
Created attachment 382568 [details] Patch
Comment on attachment 382568 [details] Patch Patch LGTM. Let's wait until all the EWS bots pass before setting cq+ :-)
Comment on attachment 382568 [details] Patch Clearing flags on attachment: 382568 Committed r251914: <https://trac.webkit.org/changeset/251914>
All reviewed patches have been landed. Closing bug.
<rdar://problem/56814353>