Automatic update from web-platform-tests RTCRtpTransceiver: introduce header extension control. This change exposes header extension control following spec details in https://w3c.github.io/webrtc-extensions/#rtcrtptransceiver-interface. Note: support for signalling directionality of header extensions in the SDP isn't implemented yet. https://chromestatus.com/feature/5680189201711104. Intent to prototype: https://groups.google.com/a/chromium.org/g/blink-dev/c/65YdUi02yZk Bug: 1051821 Change-Id: I7770fff0ebbab7ca316b811cf88da32bf5cc580c Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2597315 Commit-Queue: Markus Handell <handellm@google.com> Reviewed-by: Philip Jägenstedt <foolip@chromium.org> Reviewed-by: Harald Alvestrand <hta@chromium.org> Cr-Commit-Position: refs/heads/master@{#843998} -- wpt-commits: 3d93078c411196cf83fcc4158f479987b77a18bd wpt-pr: 26952