A recent refactoring accidentally disabled the code path that keeps
negative indices for TypedArrays on the fast path.

Change-Id: I89bbb414f54d04f85af77c6d205705906925c61e
Reviewed-on: https://chromium-review.googlesource.com/1164469Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54932}