Added FullStack performance test for screensharing with VP9

Review URL: https://codereview.webrtc.org/1215113003

Cr-Original-Commit-Position: refs/heads/master@{#9657}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 028cf488284735f949ff1edf88a5b9bf731eb184
2 files changed