Test machines are going to start checking out the source tree soon because mozharness is moving in-tree. Once they're doing that there's no point in including files that come verbatim from the source tree in the test package, it's just wasteful to download them twice. If we implement bug 917999 comment 18, then as a followup we should stop packaging files that come from the source tree and just include their relative paths in the manifest to tell mozharness to fetch them from its source checkout.
One thought: this could make it more painful to run tests from automation locally.
It's true, you'd need to have a source checkout at the same revision as the automation build. If you have a local source tree that's not particularly onerous, you just update to that revision (or pull it in first and then update). Running tests from automation already sucks, and ahal and chmanchester are going to be working on that next quarter, so hopefully the solution they come up with can paper over that.
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