Templatize percentile_filter.h and move it to base/analytics.

BUG=None

Review-Url: https://codereview.webrtc.org/2529063002
Cr-Original-Commit-Position: refs/heads/master@{#15334}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cb861e074a1988715b5d84511fecdc52b7d7091c
9 files changed