When using Chromium(48) or Chrome(45) for video chat the browsers appear to use the VP8 codec instead of VP9. Searching the Chromium WebRTC source code shows many references to the VP9 codec so I believe that it is supported.
Based on Internet searches it looks like Chrome should use the VP9 codec with WebRTC when the "--enable-webrtc-vp9-support" flag is used but I have found that this flag does not appear to have any effect with Chrome or Chromium as the SDP still indicates that VP8 is being used.
Searching the Chromium source code does not return any matches on "enable-webrtc-vp9-support" either.