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

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index efdafbb7fdf63f77b1607c3fe6f9da43f9fb6e09..861f02fcd86f0f0c8ae52c27baf54386fc0ee341 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -699,8 +699,17 @@ String getTypeExtension(Document* document,
     ElementCreationOptions impl;
     V8ElementCreationOptions::toImpl(dict.isolate(), dict.v8Value(), impl,
                                      exceptionState);
-    if (impl.hasIs())
+    if (impl.hasIs()) {
+      AtomicString type(impl.is());
+      if (document->registrationContext() &&

[dominicc (has gone to gerrit), 2016/11/16 02:46:41]

I need to see this patch based on top of yurak's patch. Sorry to ask you to slow
down, but it's hard to compute how these line up.

+          !document->registrationContext()->nameIsDefined(type) &&
+          !document->registrationContext()->v1NameIsDefined(type)) {
+        exceptionState.throwDOMException(NotFoundError,
+                                         "The type provided ('" + type + "') is not found.");
+        return emptyString();
+      }
       return impl.is();
+    }
 
     return toCoreString(dict.v8Value()->ToString());
   }