This removes the need to pass Counters into the function body decoder
by making timing happen in the callers.

R=mstarzinger@chromium.org

Change-Id: I05c8d2c85b1c315150cbf9e9b3f68efa03114b75
Reviewed-on: https://chromium-review.googlesource.com/1156700
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54842}