Implement "create an element" when sync for Custom Element V1

third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp

Index: third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp
diff --git a/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp b/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp
index ea1d265c8cbb8f2f6920e49d58ba72bef9f3ca70..9fc2d436e7b0b9e8645b9d960cec42f5ecabdd5a 100644
--- a/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp
+++ b/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistryTest.cpp
@@ -247,6 +247,16 @@ public:
         element->setCustomElementState(CustomElementState::Custom);
         return true;
     }
+
+    HTMLElement* createElementSync(Document&, const QualifiedName&) override
+    {
+        return nullptr;
+    }
+
+    HTMLElement* createElementSync(Document&, const QualifiedName&, ExceptionState&) override
+    {
+        return nullptr;
+    }
 };
 
 // Classes which use trace macros cannot be local because of the