Safely iterate over MediaStreamSource observers.

third_party/WebKit/Source/platform/mediastream/MediaStreamSource.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 35 matching lines @@
     , m_readonly(readonly)
     , m_readyState(readyState)
     , m_requiresConsumer(requiresConsumer)
 {
 }
 
 void MediaStreamSource::setReadyState(ReadyState readyState)
 {
     if (m_readyState != ReadyStateEnded && m_readyState != readyState) {
         m_readyState = readyState;
-        for (auto i = m_observers.begin(); i != m_observers.end(); ++i)
-            (*i)->sourceChangedState();
+
+        // Observers may dispatch events which create and add new Observers;
+        // take a snapshot so as to safely iterate.
+        HeapVector<Member<Observer>> observers;
+        copyToVector(m_observers, observers);
+        for (auto observer : observers)
+            observer->sourceChangedState();
     }
 }
 
 void MediaStreamSource::addObserver(MediaStreamSource::Observer* observer)
 {
     m_observers.add(observer);
 }
 
 void MediaStreamSource::addAudioConsumer(AudioDestinationConsumer* consumer)
 {
@@ skipping 29 matching lines @@
         (*it)->consumeAudio(bus, numberOfFrames);
 }
 
 DEFINE_TRACE(MediaStreamSource)
 {
     visitor->trace(m_observers);
     visitor->trace(m_audioConsumers);
 }
 
 } // namespace blink