The network control tester did not handle congestion windows correctly. Time passed when no packets were sent were not counted. This hindered the buffer delays from decreasing in congested mode. Bug: webrtc:8415 Change-Id: Id46116c6125eb5a50caa5766a3cc7291404ff920 Reviewed-on: https://webrtc-review.googlesource.com/77761 Commit-Queue: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Stefan Holmer <stefan@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23361}