[On-device adaptive brightness] Replace RingBuffer with AmbientLightSampleBuffer

RingBuffer was used to store ambient light values for modeller and adapter. This
cl replaces it with AmbientLightSampleBuffer and also related functions and
unit tests.

Bug: 881215
Change-Id: I65c16dec3a136a49f40a061d864f342f246fe95d
Reviewed-on: https://chromium-review.googlesource.com/c/1399684
Commit-Queue: Jia Meng <jiameng@chromium.org>
Reviewed-by: Michael Martis <martis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621911}
9 files changed