Where to find Dockerfile for istio-testing/protoc image?

Could someone share where to find Dockerfile for the following images?

Those’re the ones required for building istio/api, but couldn’t find under istio/test-infra repo. Maybe I’m looking at the wrong place?

Found it under tools folder of istio/api project. It’s actually not part of istio/test-infra. The istio-testing part of the image url was misleading.