The test output from https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8927983602214647664/+/steps/webkit_layout_tests_on_Windows-10-15063/0/stdout

03:24:06.717 9928 worker/0 killing secondary driver
03:24:06.892 10752 worker/4 virtual/threaded/printing/absolute-position-headers-and-footers.html output stderr lines:
03:24:06.892 10752   
03:24:06.892 10752   DevTools listening on ws://127.0.0.1:54167/devtools/browser/aa908f54-83ce-4eba-a549-aea4a36c1e90
03:24:07.167 10752 "C:\b\s\w\ir\out\Release\image_diff.exe --diff c:\b\s\w\itnxl4xd\tmptgxka0\actual.png c:\b\s\w\itnxl4xd\tmptgxka0\expected.png c:\b\s\w\itnxl4xd\tmptgxka0\diff.png" took 0.27s
03:24:07.174 10464 [4/10] virtual/threaded/printing/absolute-position-headers-and-footers.html failed unexpectedly (image diff)
03:24:07.173 10752 worker/4 virtual/threaded/printing/absolute-position-headers-and-footers.html failed:
03:24:07.174 10752 worker/4  image diff
03:24:07.174 10752 worker/4 killing secondary driver
03:24:07.225 6756 worker/2 virtual/outofblink-cors-ns/external/wpt/fetch/corb/img-html-correctly-labeled.sub.html passed
03:24:07.226 6756 worker/2 killing secondary driver
03:24:07.174 10752 worker/4 exiting
03:24:07.174 10752 worker/4 cleaning up
03:24:07.174 10752 worker/4 killing primary driver
03:24:07.308 10752 "taskkill.exe /f /t /pid 3680" took 0.13s
03:24:07.308 10752 killed pid 3680
03:24:07.309 10752 worker/4 killing secondary driver


should give more indication of what failed than just "image diff". Ideally, it should link to the before and after images.