form-associated-element-removal-expected.txt is there, but looking at the flakiness dashboard, it appears to fail MISSING sporadically. Rniwa speculates it's a problem with the webkit.py script.
Feel free to add a line to test_expectations with BUGWK72039 for this test if there isn't one already. *** This bug has been marked as a duplicate of bug 72039 ***
for the record ... in bug 72039, the working hypothesis is that for some reason the js-test-pre.js script doesn't get loaded and executed, and hence dumpAsText() is never called.