eb8b388273
Default VP9 selection is no longer triggered by field trial string after https://codereview.webrtc.org/1432673002, so VP9 need to be selected now through SDP mangling. R=wzh@webrtc.org Review URL: https://codereview.webrtc.org/1452783002 . Cr-Commit-Position: refs/heads/master@{#10660}