Add a reliability term to the echo detector.

This will ensure that the estimated likelihood starts at a low value and prevents initial spikes.

BUG=webrtc:6525

Review-Url: https://codereview.webrtc.org/2503843004
Cr-Original-Commit-Position: refs/heads/master@{#15131}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: fbb374d8ed961f055d9ec71a25e0bb77991e6ec3
3 files changed