Make legacy to perfetto conversion optional. Discard legacy traces if box selected. Useful if there's just a couple legacy dumps in a BR of otherwise perfetto traces, as conversion involves decoding the entire existing perfetto trace and re-parsing it via TP. Bug: 411363817 Test: npm run test:unit:ci Change-Id: I529b2f6b83230fc1da8f85eb1032db6f9a4d203a