Add a scoped context object for synchronous CE creation

third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp

Index: third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp b/third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp
index 98391e7f2cc4021aee338c0a9d23f41fe3e52b95..51b0d16fd1e9f030fe440f17ea8a6b48ffda4424 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp
@@ -40,6 +40,7 @@
 #include "core/dom/TemplateContentDocumentFragment.h"
 #include "core/dom/Text.h"
 #include "core/dom/custom/CEReactionsScope.h"
+#include "core/dom/custom/CustomElementCreationScope.h"
 #include "core/dom/custom/CustomElementDefinition.h"
 #include "core/dom/custom/CustomElementDescriptor.h"
 #include "core/dom/custom/CustomElementRegistry.h"
@@ -836,7 +837,10 @@ HTMLElement* HTMLConstructionSite::createHTMLElement(AtomicHTMLToken* token)
 
         // 7.
         QualifiedName elementQName(nullAtom, token->name(), HTMLNames::xhtmlNamespaceURI);
-        element = definition->createElementSync(document, elementQName);
+        {
+            CustomElementCreationScope scope(&document);
+            element = definition->createElementSync(document, elementQName);
+        }
 
         // "8. Append each attribute in the given token to element."
         // We don't use setAttributes here because the custom element