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 RunClosureWithTrace(const base::Closure& closure,
                         const char* trace_event_name) {
  TRACE_EVENT0("webrtc", trace_event_name);
  closure.Run();
}

void RunClosureWithTrace(const base::Closure& closure,
                         const char* trace_event_name) {
  TRACE_EVENT0("webrtc", trace_event_name);
  closure.Run();
}
