Have NetworkStateNotifier keep untraced ExecutionContext observers.

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

Index: third_party/WebKit/Source/core/page/NetworkStateNotifier.h
diff --git a/third_party/WebKit/Source/core/page/NetworkStateNotifier.h b/third_party/WebKit/Source/core/page/NetworkStateNotifier.h
index 1e0b7b12c70db50d29ff7d6b9d3c25ff24b337cf..91b62a0ae4c6622a43f08c9cc7767edd958eb781 100644
--- a/third_party/WebKit/Source/core/page/NetworkStateNotifier.h
+++ b/third_party/WebKit/Source/core/page/NetworkStateNotifier.h
@@ -108,7 +108,10 @@ private:
     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*);