Fix segfault when PeerConnection is destroyed during stats collection.

webrtc/api/rtcstatscollector.cc

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 412 matching lines @@
         rtc::Bind(&RTCStatsCollector::ProducePartialResultsOnNetworkThread,
             rtc::scoped_refptr<RTCStatsCollector>(this), timestamp_us));
   }
 }
 
 void RTCStatsCollector::ClearCachedStatsReport() {
   RTC_DCHECK(signaling_thread_->IsCurrent());
   cached_report_ = nullptr;
 }
 
+void RTCStatsCollector::WaitForPendingRequest() {
+  RTC_DCHECK(signaling_thread_->IsCurrent());
+  if (num_pending_partial_reports_) {
+    rtc::Thread::Current()->ProcessMessages(0);
+    while (num_pending_partial_reports_) {
+      rtc::Thread::Current()->SleepMs(1);

[Taylor Brandstetter, 2016/12/16 18:53:27]

nit: Could use an rtc::Event that's set when a partial stats report completes
instead of SleepMs.

[hbos, 2016/12/19 09:52:48]

rtc::Event's wait does not process messages. In order for
num_pending_partial_reports_ to decrease we have to do message processing (doe
to jumping to other threads for stats collecting and back to the signaling
thread for the stats report merging and invoking callback).

+      rtc::Thread::Current()->ProcessMessages(0);
+    }
+  }
+}
+
 void RTCStatsCollector::ProducePartialResultsOnSignalingThread(
     int64_t timestamp_us) {
   RTC_DCHECK(signaling_thread_->IsCurrent());
   rtc::scoped_refptr<RTCStatsReport> report = RTCStatsReport::Create(
       timestamp_us);
 
   SessionStats session_stats;
   if (pc_->session()->GetTransportStats(&session_stats)) {
     std::map<std::string, CertificateStatsPair> transport_cert_stats =
         PrepareTransportCertificateStats(session_stats);
@@ skipping 485 matching lines @@
     const std::string& type) {
   return CandidateTypeToRTCIceCandidateType(type);
 }
 
 const char* DataStateToRTCDataChannelStateForTesting(
     DataChannelInterface::DataState state) {
   return DataStateToRTCDataChannelState(state);
 }
 
 }  // namespace webrtc