Add a scoped context object for synchronous CE creation

third_party/WebKit/Source/build/scripts/templates/ElementFactory.cpp.tmpl

 {% from "macros.tmpl" import license %}
 {{ license() }}
 
 #include "{{namespace}}ElementFactory.h"
 
 #include "{{namespace}}Names.h"
 {% for tag in tags|groupby('interface') %}
 #include "core/{{namespace|lower}}/{{tag[0]}}.h"
 {% endfor %}
 {% if fallback_interface %}
 #include "core/{{namespace|lower}}/{{fallback_interface}}.h"
 {% endif %}
 {% if namespace == 'HTML' %}
 #include "core/dom/custom/CustomElement.h"
+#include "core/dom/custom/CustomElementCreationScope.h"
 {% endif %}
 #include "core/dom/custom/V0CustomElement.h"
 #include "core/dom/custom/V0CustomElementRegistrationContext.h"
 #include "core/dom/Document.h"
 #include "core/frame/Settings.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "wtf/HashMap.h"
 
 namespace blink {
 
@@ skipping 62 matching lines @@
     if (!g_constructors)
         create{{namespace}}FunctionMap();
     if (ConstructorFunction function = g_constructors->get(localName))
         return function(document, {% if namespace == 'HTML' %}formElement, {% endif %}flags);
 
     {% if namespace == 'HTML' %}
     if (CustomElement::shouldCreateCustomElement(localName)) {
         QualifiedName tagName(nullAtom, localName, HTMLNames::xhtmlNamespaceURI);
         if (flags & AsynchronousCustomElements)
             return CustomElement::createCustomElementAsync(document, tagName);
+        CustomElementCreationScope scope(&document);
         return CustomElement::createCustomElementSync(document, tagName);
     }
     {% endif %}
 
     if (document.registrationContext() && V0CustomElement::isValidName(localName)) {
         Element* element = document.registrationContext()->createCustomTagElement(document, QualifiedName(nullAtom, localName, {{namespace_prefix}}NamespaceURI));
         ASSERT_WITH_SECURITY_IMPLICATION(element->is{{namespace}}Element());
         return to{{namespace}}Element(element);
     }
 
     return {{fallback_interface}}::create(QualifiedName(nullAtom, localName, {{namespace_prefix}}NamespaceURI), document);
 }
 
 } // namespace blink