Destroy WebRTCStatsReportCallbackResolver on main thread, fixes crash.

third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 375 matching lines @@
 // |RTCPeerConnection::getStats(ScriptState*, MediaStreamTrack*)|
 class WebRTCStatsReportCallbackResolver : public WebRTCStatsReportCallback {
  public:
   // Takes ownership of |resolver|.
   static std::unique_ptr<WebRTCStatsReportCallback> create(
       ScriptPromiseResolver* resolver) {
     return std::unique_ptr<WebRTCStatsReportCallback>(
         new WebRTCStatsReportCallbackResolver(resolver));
   }
 
-  ~WebRTCStatsReportCallbackResolver() override {}
+  ~WebRTCStatsReportCallbackResolver() override {
+    DCHECK(
+        m_resolver->getScriptState()->getExecutionContext()->isContextThread());
+  }
 
  private:
   WebRTCStatsReportCallbackResolver(ScriptPromiseResolver* resolver)
       : m_resolver(resolver) {}
 
   void OnStatsDelivered(std::unique_ptr<WebRTCStatsReport> report) override {
+    DCHECK(
+        m_resolver->getScriptState()->getExecutionContext()->isContextThread());
     m_resolver->resolve(new RTCStatsReport(std::move(report)));
   }
 
   Persistent<ScriptPromiseResolver> m_resolver;
 };
 
 }  // namespace
 
 RTCPeerConnection::EventWrapper::EventWrapper(
     Event* event,
@@ skipping 1087 matching lines @@
 DEFINE_TRACE(RTCPeerConnection) {
   visitor->trace(m_localStreams);
   visitor->trace(m_remoteStreams);
   visitor->trace(m_dispatchScheduledEventRunner);
   visitor->trace(m_scheduledEvents);
   EventTargetWithInlineData::trace(visitor);
   SuspendableObject::trace(visitor);
 }
 
 }  // namespace blink