Nested <use>s can resolve against an external resource

third_party/WebKit/Source/core/svg/SVGUseElement.h

Index: third_party/WebKit/Source/core/svg/SVGUseElement.h
diff --git a/third_party/WebKit/Source/core/svg/SVGUseElement.h b/third_party/WebKit/Source/core/svg/SVGUseElement.h
index 274fb33568ad89cb0c0041b103838af18fc47121..eff2c0e3b00879d6b0ea49fe452c41957290cc2f 100644
--- a/third_party/WebKit/Source/core/svg/SVGUseElement.h
+++ b/third_party/WebKit/Source/core/svg/SVGUseElement.h
@@ -95,12 +95,16 @@ class SVGUseElement final : public SVGGraphicsElement,
   }
 
   // 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();