After r138724, WebKit1.MemoryCachePruneWithinResourceLoadDelegate started to failing intermittently.
The code changed in the said revision is never ran nor is ImageLoader ever created.
Tools/Scripts/run-api-tests --debug WebKit1\.MemoryCacheDisableWithinResourceLoadDelegate WebKit1\.MemoryCachePruneWithinResourceLoadDelegate
Temporarily disabled the test in http://trac.webkit.org/changeset/138753 for now.
This started failing slightly earlier, actually, sometime before r138718 at least:
That bot's last successful run was at r138707.
I'm able to reproduce this back to r138700, fwiw.