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

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

Index: third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h b/third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h
index 6423d5ad6b2477f8b6b3c67b064cb87a6b814362..4dda878fed1a4848d156c2c7c9cbd2608f99ceb7 100644
--- a/third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLFrameOwnerElement.h
@@ -109,21 +109,25 @@ 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;