old-run-webkit-tests reads the wrong PNG checksum if a more-platform-specific PNG has an embedded checksum but a less-platform-specific PNG does not
Created attachment 90237 [details] Make old-run-webkit-tests prefer embedded checksums to out-of-line .checksum files
Tony convinced me we don't want to do this until more checked-in PNGs have embedded checksums. Otherwise we might slow down the tests!