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}
RTCPeerConnectionHandler::FindSender(uintptr_t id) {
  for (auto it = rtp_senders_.begin(); it != rtp_senders_.end(); ++it) {
    if ((*it)->Id() == id)
      return it;
  }
  return rtp_senders_.end();
}

RTCPeerConnectionHandler::FindSender(uintptr_t id) {
  for (auto it = rtp_senders_.begin(); it != rtp_senders_.end(); ++it) {
    if ((*it)->Id() == id)
      return it;
  }
  return rtp_senders_.end();
}
