Check weak pointers in RTCPeerConnectionHandler::WebRtcSetDescriptionObserverImpl

Bug: 912074
Change-Id: I8ba86751f5d5bf12db51520f985ef0d3dae63ed8
Reviewed-on: https://chromium-review.googlesource.com/c/1411916
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622945}
void RTCPeerConnectionHandler::GetStats(
    std::unique_ptr<blink::WebRTCStatsReportCallback> callback,
    blink::RTCStatsFilter filter) {
  DCHECK(task_runner_->RunsTasksInCurrentSequence());
  signaling_thread()->PostTask(
      FROM_HERE,
      base::BindOnce(&GetRTCStatsOnSignalingThread, task_runner_,
                     native_peer_connection_, std::move(callback), filter));
}

void RTCPeerConnectionHandler::GetStats(
    std::unique_ptr<blink::WebRTCStatsReportCallback> callback,
    blink::RTCStatsFilter filter) {
  DCHECK(task_runner_->RunsTasksInCurrentSequence());
  signaling_thread()->PostTask(
      FROM_HERE,
      base::BindOnce(&GetRTCStatsOnSignalingThread, task_runner_,
                     native_peer_connection_, std::move(callback), filter));
}
