Don't reset LoadEventProgress if frame unload has already started.

third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 91 matching lines @@
     RawPtrWillBeMember<Frame> m_contentFrame;
     RefPtrWillBeMember<Widget> m_widget;
     SandboxFlags m_sandboxFlags;
 };
 
 DEFINE_ELEMENT_TYPE_CASTS(HTMLFrameOwnerElement, isFrameOwnerElement());
 
 class SubframeLoadingDisabler {
     STACK_ALLOCATED();
 public:
-    explicit SubframeLoadingDisabler(Node& root)
+    explicit SubframeLoadingDisabler(Node& root) : SubframeLoadingDisabler(&root)
+    {
+    }
+
+    explicit SubframeLoadingDisabler(Node* root)
         : m_root(root)
     {
-        disabledSubtreeRoots().add(m_root);
+        if (m_root)
+            disabledSubtreeRoots().add(m_root);
     }
 
     ~SubframeLoadingDisabler()
     {
-        disabledSubtreeRoots().remove(m_root);
+        if (m_root)
+            disabledSubtreeRoots().remove(m_root);
     }
 
     static bool canLoadFrame(HTMLFrameOwnerElement& owner)
     {
-        if (owner.document().unloadStarted())
-            return false;
         for (Node* node = &owner; node; node = node->parentOrShadowHostNode()) {
             if (disabledSubtreeRoots().contains(node))
                 return false;
         }
         return true;
     }
 
 private:
-    static WillBeHeapHashCountedSet<RawPtrWillBeMember<Node>>& disabledSubtreeRoots();
+    CORE_EXPORT static WillBeHeapHashCountedSet<RawPtrWillBeMember<Node>>& disabledSubtreeRoots();
 
     RawPtrWillBeMember<Node> m_root;
 };
 
 DEFINE_TYPE_CASTS(HTMLFrameOwnerElement, FrameOwner, owner, owner->isLocal(), owner.isLocal());
 
 } // namespace blink
 
 #endif // HTMLFrameOwnerElement_h