Track connected subframes per-Document instead of per-Node.

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index 74809e791f3ba0173bbb90859181bb3240af1fe5..46ad99377025a311477cccc6cceed170b7ca52f6 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -42,6 +42,7 @@
 #include "core/dom/DocumentTiming.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/MutationObserver.h"
+#include "core/dom/SubframeTracker.h"
 #include "core/dom/TextLinkColors.h"
 #include "core/dom/TreeScope.h"
 #include "core/dom/UserActionElementSet.h"
@@ -1054,6 +1055,8 @@ public:
     }
     int nodeCount() const { return m_nodeCount; }
 
+    SubframeTracker& subframeTracker() { return m_subframeTracker; }
+
     using WeakDocumentSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<Document>>;
     static WeakDocumentSet& liveDocumentSet();
 
@@ -1233,6 +1236,8 @@ private:
     using AttachedRangeSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<Range>>;
     AttachedRangeSet m_ranges;
 
+    SubframeTracker m_subframeTracker;
+
     unsigned short m_listenerTypes;
 
     MutationObserverOptions m_mutationObserverTypes;