This patch cleans up the rest of our custom casting helper
functions.

Change-Id: I41975c736765fca855c4498acca31116df3e8317
Reviewed-on: https://chromium-review.googlesource.com/263477Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>