Bug 1957689 - Fix detection of cross-doc references.

MANUAL PUSH: Orange fix CLOSED TREE

dom/base/IDTracker.cpp

@@ -140,7 +140,11 @@ static nsIURI* GetExternalResourceURIIfNeeded(nsIURI* aBaseURI,
   if (!use) {
     return nullptr;
   }
-  nsIURI* originalURI = use->GetSourceDocURI();
+  Document* doc = use->GetSourceDocument();
+  if (!doc || doc == aFrom.OwnerDoc()) {
+    return nullptr;
+  }
+  nsIURI* originalURI = doc->GetDocumentURI();
   if (!originalURI) {
     return nullptr;
   }

dom/base/IDTracker.h

@@ -51,7 +51,7 @@ class IDTracker {
   /**
    * Find which element, if any, is referenced.
    */
-  Element* get() { return mElement; }
+  Element* get() const { return mElement; }
 
   /**
    * Set up a reference to another element, identified by the fragment

dom/svg/SVGUseElement.cpp

@@ -485,22 +485,19 @@ void SVGUseElement::UpdateShadowTree() {
   targetElement->AddMutationObserver(this);
 }
 
-nsIURI* SVGUseElement::GetSourceDocURI() {
+Document* SVGUseElement::GetSourceDocument() const {
   nsIContent* targetElement = mReferencedElementTracker.get();
-  if (!targetElement) {
-    return nullptr;
-  }
-
-  return targetElement->OwnerDoc()->GetDocumentURI();
+  return targetElement ? targetElement->OwnerDoc() : nullptr;
 }
 
-const Encoding* SVGUseElement::GetSourceDocCharacterSet() {
-  nsIContent* targetElement = mReferencedElementTracker.get();
-  if (!targetElement) {
-    return nullptr;
-  }
+nsIURI* SVGUseElement::GetSourceDocURI() const {
+  auto* doc = GetSourceDocument();
+  return doc ? doc->GetDocumentURI() : nullptr;
+}
 
-  return targetElement->OwnerDoc()->GetDocumentCharacterSet();
+const Encoding* SVGUseElement::GetSourceDocCharacterSet() const {
+  auto* doc = GetSourceDocument();
+  return doc ? doc->GetDocumentCharacterSet() : nullptr;
 }
 
 static nsINode* GetClonedChild(const SVGUseElement& aUseElement) {

dom/svg/SVGUseElement.h

@@ -80,8 +80,9 @@ class SVGUseElement final : public SVGUseElementBase,
   already_AddRefed<DOMSVGAnimatedLength> Width();
   already_AddRefed<DOMSVGAnimatedLength> Height();
 
-  nsIURI* GetSourceDocURI();
-  const Encoding* GetSourceDocCharacterSet();
+  Document* GetSourceDocument() const;
+  nsIURI* GetSourceDocURI() const;
+  const Encoding* GetSourceDocCharacterSet() const;
   URLExtraData* GetContentURLData() const { return mContentURLData; }
 
   // Updates the internal shadow tree to be an up-to-date clone of the