If 'is' is not null and custom element definition not found, NotFoundError should be thrown

third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp

Index: third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp
diff --git a/third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp b/third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp
index 01e63b3d3b4f3693998e7cba41be6caf0e4e662e..ef34ae3ecbe9730dbe948ae265205bc630d21bb2 100644
--- a/third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp
+++ b/third_party/WebKit/Source/core/dom/custom/V0CustomElementRegistrationContext.cpp
@@ -177,6 +177,11 @@ void V0CustomElementRegistrationContext::setV1(
   m_registry.setV1(v1);
 }
 
+bool V0CustomElementRegistrationContext::v1NameIsDefined(
+    const AtomicString& name) const {
+  return m_registry.v1NameIsDefined(name);
+}
+
 DEFINE_TRACE(V0CustomElementRegistrationContext) {
   visitor->trace(m_candidates);
   visitor->trace(m_registry);