When triggering buildbucket build, I set:

"parameters_json": "{\"builder_name\": \"Linux Tests SANDBOX\", \"parent_buildername\": \"Linux Builder SANDBOX\", ...}"

I can see these here
https://logs.chromium.org/v/?s=chromium%2Fled%2Ftandrii_google.com%2Ff0e18da5fdc4f69c205210d390c18daccbd1eddcb3ba1c28d8d03ad77685bf35%2F%2B%2Fsteps%2Ftrigger%2F0%2Flogs%2Fjson.output%2F0
and here 
https://apis-explorer.appspot.com/apis-explorer/?base=https://cr-buildbucket.appspot.com/_ah/api#p/buildbucket/v1/buildbucket.get?id=8962898691676253792&_h=1&

However actual build recipe property is missing:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20SANDBOX/13