Break up ReadProtoJsonFile function into 2 functions due to failures in https://crrev.com/c/6449947

Change-Id: I5c2b858797a85b0dfbdf7c41d5d115cbcda2e99d
Bug: b/399765201, b/399765200
Test: unittest
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/6520873
Reviewed-by: Allen Xie <zhihuixie@google.com>
Reviewed-by: Jason Kusuma <jkusuma@google.com>
Tested-by: Charlotte Chan <lottechan@google.com>
Commit-Queue: Charlotte Chan <lottechan@google.com>
2 files changed