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

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 664 matching lines @@
     AtomicString localName = convertLocalName(name);
     if (CustomElement::shouldCreateCustomElement(localName))
       return CustomElement::createCustomElementSync(*this, localName);
     return HTMLElementFactory::createHTMLElement(localName, *this, 0,
                                                  CreatedByCreateElement);
   }
 
   return Element::create(QualifiedName(nullAtom, name, nullAtom), this);
 }
 
 String getTypeExtension(Document* document,

[dominicc (has gone to gerrit), 2016/11/08 08:48:36]

I'm pretty sure this isn't how we should implement this. For example, step 4 is
also meant to use the local name in the lookup. Step 7 could use the custom
element definition and skip a lookup step that otherwise happens twice.

The existence of custom elements v0 does complicate things somewhat though :/

Could you send email to yurak with a pointer to this patch and work out the
details with her? She's working in this area, see eg
https://codereview.chromium.org/2477713003

                         const StringOrDictionary& stringOrOptions,
                         ExceptionState& exceptionState) {
   if (stringOrOptions.isNull())
     return emptyString();
 
   if (stringOrOptions.isString()) {
     UseCounter::count(document,
                       UseCounter::DocumentCreateElement2ndArgStringHandling);
     return stringOrOptions.getAsString();
   }
 
   if (stringOrOptions.isDictionary()) {
     Dictionary dict = stringOrOptions.getAsDictionary();
     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());
   }
 
   return emptyString();
 }
 
 Element* Document::createElement(const AtomicString& localName,
                                  const StringOrDictionary& stringOrOptions,
                                  ExceptionState& exceptionState) {
@@ skipping 5750 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif