Since 262812@main we are creating the accelerated surface from drawing area constructor, but WebPage is setting the device scale factor after creating the drawing area, so we end up using the unscaled size.
Pull request: https://github.com/WebKit/WebKit/pull/12647
Committed 262867@main (b762cdb7aea0): <https://commits.webkit.org/262867@main> Reviewed commits have been landed. Closing PR #12647 and removing active labels.