[On-device adaptive brightness] Implement average log ALS

If flag average_log_als is true, we will use average log ALS values for model
training (modeller) and inference (adapter). In this case, darkening and
brightening thresholds will be calculated relative to average log ALS too.

Bug: 881215
Change-Id: Icd55e6ecdbec8118666631ec8e9fbf4dd019e68c
Reviewed-on: https://chromium-review.googlesource.com/c/1401824
Commit-Queue: Jia Meng <jiameng@chromium.org>
Reviewed-by: Michael Martis <martis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622363}
6 files changed