Use RaceChecker instead of ThreadChecker in remote_bitrate_estimator. BUG=webrtc:7826 Review-Url: https://codereview.webrtc.org/3006173002 Cr-Original-Commit-Position: refs/heads/master@{#19778} Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc Cr-Mirrored-Commit: 423227306112c4011a538bf87ae7f2534f39f724