In Bug 209516 WebGL 2.0-specific validation was added to ANGLE for pixel unpack parameters. While upstreaming that fix in http://crbug.com/angleproject/4849 a small error was found which should be merged into WebKit as well.
Created attachment 404617 [details] Patch
Note that there are important steps to take when updating ANGLE. See http://trac.webkit.org/wiki/UpdatingANGLE
Comment on attachment 404617 [details] Patch ANGLE patch has landed upstream. CQ'ing again.
Committed r264562: <https://trac.webkit.org/changeset/264562> All reviewed patches have been landed. Closing bug and clearing flags on attachment 404617 [details].
<rdar://problem/65753880>