Now duplicate parameter detection depends on tracking of unresolved references.
This also fixes finding duplicate parameters of arrow functions nested in other
arrow functions.

Change-Id: I644bfdc513244637345c1069e5c7e5fde713da63
Reviewed-on: https://chromium-review.googlesource.com/c/1270578
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56467}