The test would flake using a real clock since time may pass between
calls to PostDelayedTask which would result in the tasks running
out of the expected order.
Bug: webrtc:11208, webrtc:11219
Change-Id: Ice5fe6ec4e9bf2ce89f00c6de7ed06b89dbe88cc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/162100
Reviewed-by: Yves Gerey <yvesg@google.com>
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30101}
094396fb76