Fix a typo in WebrtcVideoStream::Start() which causes the host to crash.

When landing https://codereview.chromium.org/1571543002 a last-minute
change was made to address review comment in webrtc_video_stream.cc
and the change wasn't properly validated.

Review URL: https://codereview.chromium.org/1578253004

Cr-Commit-Position: refs/heads/master@{#369080}
1 file changed