Use Android log system in helpers.c.

Use Android log system in helpers.c.

This code might be loaded by a daemonized process now, so the existing
logging to stderr goes nowhere. It's better to use the Android logger.

Change-Id: I19f088b8f049f07c9c6839038d2971fad1a0e852
Reviewed-on: https://chromium-review.googlesource.com/971360
Commit-Ready: Alistair Strachan <astrachan@google.com>
Tested-by: Alistair Strachan <astrachan@google.com>
Reviewed-by: Alistair Strachan <astrachan@google.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>