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
24 files changed