Nested <use>s can resolve against an external resource

third_party/WebKit/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.
  *
@@ skipping 77 matching lines @@
   }
 
   bool SelfHasRelativeLengths() const override;
 
   ShadowRoot& UseShadowRoot() const {
     CHECK(ClosedShadowRoot());
     return *ClosedShadowRoot();
   }
 
   // Instance tree handling
-  Element* ResolveTargetElement();
+  enum ObserveBehavior {
+    kAddObserver,
+    kDontAddObserver,
+  };
+  Element* ResolveTargetElement(ObserveBehavior);
   void BuildShadowAndInstanceTree(SVGElement& target);
   void ClearInstanceRoot();
   Element* CreateInstanceTree(SVGElement& target_root) const;
   void ClearResourceReference();
-  bool HasCycleUseReferencing(const SVGUseElement&,
+  bool HasCycleUseReferencing(SVGUseElement&,
                               const ContainerNode& target_instance,
                               SVGElement*& new_target) const;
   bool ExpandUseElementsInShadowTree();
   void CloneNonMarkupEventListeners();
   void AddReferencesToFirstDegreeNestedUseElements(SVGElement& target);
 
   void InvalidateDependentShadowTrees();
 
   bool ResourceIsStillLoading() const;
   bool ResourceIsValid() const;
@@ skipping 13 matching lines @@
   bool have_fired_load_event_;
   bool needs_shadow_tree_recreation_;
   Member<SVGElement> target_element_instance_;
   Member<IdTargetObserver> target_id_observer_;
   Member<DocumentResource> resource_;
 };
 
 }  // namespace blink
 
 #endif  // SVGUseElement_h