This directory is included in the proto import path. It contains well-known proto files not included in the protobuf compiler itself. The reason it exists is luci-go repo does not have a mechanism to declare dependencies on other repositories.
./google/api contents were copied from https://github.com/googleapis/googleapis/tree/54082ac49c31bb8417cec3227c6f52a8bc35fa0f/google/api
./google/rpc contents were copied from https://github.com/googleapis/googleapis/tree/943102cfb5fa8811a15a4c21bd12421aadb423b5/google/rpc
./google/type contents were copied from https://github.com/googleapis/googleapis/tree/943102cfb5fa8811a15a4c21bd12421aadb423b5/google/type