replMode and awaitPromise are mutually exclusive in Chrome — under replMode a
returned promise serialises to {} instead of being awaited, which broke every
fetch/async eval (e2e_domain_filter, e2e_headers, e2e_react_tree all regressed).
Enable replMode only for synchronous scripts that declare a top-level let/const
(the #38 case); promise-returning scripts keep awaitPromise — restoring the
pre-#38 await behaviour while still fixing the let-redeclaration collision.
leeguooooo
c47601bd7b