Don't transfer viewport to an invalid/dirty <use> instance

Source/core/svg/SVGUseElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  *
  * 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,
@@ skipping 58 matching lines @@
 
     bool isStructurallyExternal() const override { return !hrefString().isNull() && isExternalURIReference(hrefString(), document()); }
 
     InsertionNotificationRequest insertedInto(ContainerNode*) override;
     void removedFrom(ContainerNode*) override;
 
     void svgAttributeChanged(const QualifiedName&) override;
 
     LayoutObject* createLayoutObject(const ComputedStyle&) override;
 
-    void clearResourceReferences();
-    void buildShadowAndInstanceTree(SVGElement* target);
-
     void scheduleShadowTreeRecreation();
+    void cancelShadowTreeRecreation();
     bool haveLoadedRequiredResources() override { return !isStructurallyExternal() || m_haveFiredLoadEvent; }
 
     bool selfHasRelativeLengths() const override;
 
     // Instance tree handling
+    void buildShadowAndInstanceTree(SVGElement* target);
+    void clearInstanceRoot();
     bool buildShadowTree(SVGElement* target, SVGElement* targetInstance, bool foundUse);
+    void clearShadowTree();
     bool hasCycleUseReferencing(SVGUseElement*, ContainerNode* targetInstance, SVGElement*& newTarget);
     bool expandUseElementsInShadowTree(SVGElement*);
     void expandSymbolElementsInShadowTree(SVGElement*);
 
     void transferUseAttributesToReplacedElement(SVGElement* from, SVGElement* to) const;
 
     void invalidateDependentShadowTrees();
 
     bool resourceIsStillLoading();
     Document* externalDocument() const;
     bool instanceTreeIsLoading(SVGElement*);
     void notifyFinished(Resource*) override;
     TreeScope* referencedScope() const;
     void setDocumentResource(ResourcePtr<DocumentResource>);
 
     RefPtrWillBeMember<SVGAnimatedLength> m_x;
     RefPtrWillBeMember<SVGAnimatedLength> m_y;
     RefPtrWillBeMember<SVGAnimatedLength> m_width;
     RefPtrWillBeMember<SVGAnimatedLength> m_height;
 
     bool m_haveFiredLoadEvent;
     bool m_needsShadowTreeRecreation;
     RefPtrWillBeMember<SVGElement> m_targetElementInstance;
     ResourcePtr<DocumentResource> m_resource;
 };
 
 } // namespace blink
 
 #endif // SVGUseElement_h