Code:    void ProcessStateChangesPlanB(WebRtcSetDescriptionObserver::States states) {
     DCHECK_EQ(sdp_semantics_, webrtc::SdpSemantics::kPlanB);
     std::vector<RTCRtpReceiver*> removed_receivers;
    for (auto it = handler_->rtp_receivers_.begin();
         it != handler_->rtp_receivers_.end(); ++it) {
      if (ReceiverWasRemoved(*(*it), states.transceiver_states))
        removed_receivers.push_back(it->get());
    }
 
     for (auto& transceiver_state : states.transceiver_states) {
      if (ReceiverWasAdded(transceiver_state)) {
         handler_->OnAddReceiverPlanB(transceiver_state.MoveReceiverState());
       }
     }
     for (auto* removed_receiver : removed_receivers) {
      handler_->OnRemoveReceiverPlanB(RTCRtpReceiver::getId(
          removed_receiver->state().webrtc_receiver().get()));
     }
   }

Vulnerability Type: 
CWE ID: CWE-416
Summary: Insufficient checks of pointer validity in WebRTC in Google Chrome prior to 72.0.3626.81 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
Commit Message: 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}