Old config events are no longer removed from RtcEventLog.

Time to keep old events in buffer is now changeable at runtime.
Added unit test for removing old events from buffer.

Review URL: https://codereview.webrtc.org/1303713002

Cr-Original-Commit-Position: refs/heads/master@{#10302}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1adce14c87f8316b5c3f4ee16b8f573c8bf14761
3 files changed