Ok so it looks like we already have two copies of this code: 

one in third_party:

https://cs.chromium.org/chromium/src/third_party/skia/infra/bots/recipe_modules/swarming/resources/results_merger.py?q=results_merger&sq=package:chromium&dr=C&l=121

And one in swarming resources:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/swarming/resources/results_merger.py?q=results_merger&sq=package:chromium&dr=C&l=122

I am assuming we would only move the one instance owned by infra.

John are you ok with the move?  It means that standard_isolated_script_merge.py (https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/swarming/resources/standard_isolated_script_merge.py?q=StandardIsolatedScriptMerge&sq=package:chromium&dr=CSs&l=14) would have to invoke the src side script. 

How do you envision the standard_isolated_script_merge.py invoking the merger script from src? What happens if it can't find it, or if it isn't provided?

Why can't we just call a subprocess to a standard location on src side?

This bug has an owner, thus, it's been triaged. Changing status to "assigned".