Working with chromium/v8, I can honestly say google's code search infra is one of the most valuable resources available. I really hope they open source the backend at some point.
As for UI, treetide/underhood I mention elsewhere is the only open option now.
But Kythe comes with command line utils and an API you can query directly as well.
What is missing from the open source is a production-ready parallel serving table builder. There is one in golang which uses Apache Beam, but last time I checked the go workers are not well supported on the Flink runner. It didn't even work properly on the GCP runner. Hope this would change.