You’re rather underestimating the vast expanse that is the Chromium codebase, I think. That said, distributing tags files was a common thing once, and a dedicated symbol package you could just download and feed into your language server (instead of being constantly tethered to a symbol server) could make for a nice affordance today.
So this actually exists, as it turns out. You can run clangd-indexer to produce a static index and then load it with clangd -index-file. The caveat is that
> [r]unning clangd-indexer is expensive and produced index is not incremental.
