the app's xcallback URL defined in tests' .plist files are not the identical depending on whether we build with GN or with GYP:

GYP takes the target's name and removes all the underscores ('>!(echo ">(_target_name)" | sed -e "s/_//g")'), while GN seems to take the target's name as it is.

Example:
With GN the plist contains chromekifwebtests-x-callback
With GYP the plist contains chrome_kif_webtests-x-callback