Have NetworkStateNotifier keep untraced ExecutionContext observers.

third_party/WebKit/Source/core/page/NetworkStateNotifier.h

 /*
  * Copyright (C) 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 90 matching lines @@
         {
         }
         bool iterating;
         Vector<NetworkStateObserver*> observers;
         Vector<size_t> zeroedObservers; // Indices in observers that are 0.
     };
 
     void setWebConnectionImpl(WebConnectionType, double maxBandwidthMbps);
     void setMaxBandwidthImpl(double maxBandwidthMbps);
 
-    using ObserverListMap = WillBePersistentHeapHashMap<RawPtrWillBeWeakMember<ExecutionContext>, OwnPtr<ObserverList>>;
+    // The ObserverListMap is cross-thread accessed, adding/removing Observers running
+    // within an ExecutionContext. Kept off-heap to ease cross-thread allocation and use;
+    // the observers are (already) responsible for explicitly unregistering while finalizing.
+    using ObserverListMap = HashMap<RawPtrWillBeUntracedMember<ExecutionContext>, OwnPtr<ObserverList>>;
 
     void notifyObserversOfConnectionChangeOnContext(WebConnectionType, double maxBandwidthMbps, ExecutionContext*);
 
     ObserverList* lockAndFindObserverList(ExecutionContext*);
 
     // Removed observers are nulled out in the list in case the list is being
     // iterated over. Once done iterating, call this to clean up nulled
     // observers.
     void collectZeroedObservers(ObserverList*, ExecutionContext*);
 
     mutable Mutex m_mutex;
     bool m_isOnLine;
     WebConnectionType m_type;
     double m_maxBandwidthMbps;
     ObserverListMap m_observers;
     bool m_testUpdatesOnly;
 };
 
 CORE_EXPORT NetworkStateNotifier& networkStateNotifier();
 
 } // namespace blink
 
 #endif // NetworkStateNotifier_h