Since SubimageCacheWithTimer caches sub images of a CGImage only, rename it CGSubimageCacheWithTimer. Then we can use CachedSubimage for caching a sub image of an Image.
<rdar://problem/104980275>
Pull request: https://github.com/WebKit/WebKit/pull/9562
Committed 259817@main (dcd501fb2a54): <https://commits.webkit.org/259817@main> Reviewed commits have been landed. Closing PR #9562 and removing active labels.