Store 'length' and 'formal_parameter_count' fields as raw ints.
Also fixed a couple of issues on the way.

TBR=verwaest@chromium.org

Bug: v8:6470
Change-Id: I74ecd87cb0f041e61dab50d8bc29e3604dd1d09c
Reviewed-on: https://chromium-review.googlesource.com/527156
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45774}