LibWeb: Move SVGElement's dataset construction to initialize()

It's not safe to allocate new cells while in a cell constructor.

Userland/Libraries/LibWeb/SVG/SVGElement.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/HTML/DOMStringMap.h>
 #include <LibWeb/SVG/SVGElement.h>
@@ -12,7 +13,6 @@ namespace Web::SVG {
 
 SVGElement::SVGElement(DOM::Document& document, DOM::QualifiedName qualified_name)
     : Element(document, move(qualified_name))
-    , m_dataset(HTML::DOMStringMap::create(*this).release_value_but_fixme_should_propagate_errors())
 {
 }
 
@@ -21,13 +21,17 @@ JS::ThrowCompletionOr<void> SVGElement::initialize(JS::Realm& realm)
     MUST_OR_THROW_OOM(Base::initialize(realm));
     set_prototype(&Bindings::ensure_web_prototype<Bindings::SVGElementPrototype>(realm, "SVGElement"));
 
+    m_dataset = TRY(Bindings::throw_dom_exception_if_needed(realm.vm(), [&]() {
+        return HTML::DOMStringMap::create(*this);
+    }));
+
     return {};
 }
 
 void SVGElement::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
-    visitor.visit(m_dataset.ptr());
+    visitor.visit(m_dataset);
 }
 
 }

Userland/Libraries/LibWeb/SVG/SVGElement.h

@@ -25,7 +25,7 @@ protected:
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
-    JS::NonnullGCPtr<HTML::DOMStringMap> m_dataset;
+    JS::GCPtr<HTML::DOMStringMap> m_dataset;
 };
 
 }