User reported issue. Lock file issues should pop up here:
https://cs.chromium.org/chromium/src/content/browser/indexed_db/indexed_db_backing_store.cc?l=955

And we should be sending the error back here:
https://cs.chromium.org/chromium/src/content/browser/indexed_db/indexed_db_factory_impl.cc?type=cs&l=592

There isn't a repro here, but I'll take a look at the code to see where things might be falling through the cracks, and try to trigger some fake lockfile issues to see if we get a correct callback.