Add screenshare perf tests with lossy links

This is a re-land of https://codereview.webrtc.org/1409513005/
Fingers crossed, the problems previously seen have been resolved by
https://codereview.webrtc.org/1412233003/

BUG=

Review URL: https://codereview.webrtc.org/1409993011

Cr-Original-Commit-Position: refs/heads/master@{#10751}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: ee37de3c13c5fe4b397d909918e9f980dc8184c5
2 files changed