This is a reland of https://codereview.webrtc.org/1385563005 which was reverted since the test was flaky. The reason was a race condition (in the test) and that NACK wasn't properly set up. BUG= Review URL: https://codereview.webrtc.org/1406193002 Cr-Commit-Position: refs/heads/master@{#10303}