Specifically, I'm moving histogram_percentile_counter.h mathutils.h mod_ops.h moving_max_counter.h They shouldn't be part of the API, and moving them to an appropriate subdirectory of rtc_base/ is a good way to keep track of that. BUG=webrtc:8445 Change-Id: I78a999984a27ef935be2d7c3136475d5f209adda Reviewed-on: https://webrtc-review.googlesource.com/20870 Commit-Queue: Karl Wiberg <kwiberg@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20832}