This fixes an issue where SendSideCongestionControllerTest.OldFeedback calls a function that posts a task on a TaskQueue and immediately after changes the mocked observer that is called from that task. Bug: webrtc:10056 Change-Id: Ib1cca5bf695482e75106bfc715662e4f76c381d9 Reviewed-on: https://webrtc-review.googlesource.com/c/112940 Reviewed-by: Björn Terelius <terelius@webrtc.org> Commit-Queue: Sebastian Jansson <srte@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25882}