The ShareableBitmapCG aligns the rows using IOSurfaceAlignProperty(kIOSurfaceBytesPerRow, ...). This means the default implementation which is "width x 4" is wrong for ImageBufferShareableBitmapBackend. This will fix the layout failure: fast/canvas/canvas-large-dimensions.html [ Failure ]
Created attachment 421390 [details] Patch
Committed r273406: <https://commits.webkit.org/r273406> All reviewed patches have been landed. Closing bug and clearing flags on attachment 421390 [details].
<rdar://problem/74700179>