Add helper for loading files, use let

Bug: skia:
Change-Id: I2da7325f5cfbd451358e183e24dcf21278615eb0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206200
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed