It's used to cache the presence two gl extensions that could be cached and provided by the GLContext which also makes easier to create bitmap textures.
Pull request: https://github.com/WebKit/WebKit/pull/19945
Committed 270173@main (b01c2d6d038a): <https://commits.webkit.org/270173@main> Reviewed commits have been landed. Closing PR #19945 and removing active labels.
<rdar://problem/117905120>