http/tests/loading/preload-img-test.html seems to be failing on Windows. It started failing after r47148, but it seems extremely unlikely that that revision actually caused the failure.
I've added the test to the Skipped file for now.
I did some investigation of this today. I can reproduce the failure like this:
run-webkit-tests http/tests/incremental/split-hex-entities.pl http/tests/loading/bad-server-subframe.html http/tests/loading/preload-img-test.html
Removing either of the first two tests makes the failure go away.
The test seems to be failing because the synchronous XHR to load /resources/network-simulator.php?command=reset-resource-count is timing out. The resource count never gets reset, so the old value from the last time the tests was run is maintained.
This may be related to bug 30392.