Fix upgrading built-in custom elements

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/custom/CustomElementRegistry.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptCustomElementDefinitionBuilder.h"
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
@@ skipping 252 matching lines @@
     const AtomicString& name) const {
   return DefinitionForId(name_id_map_.at(name));
 }
 
 CustomElementDefinition* CustomElementRegistry::DefinitionForId(
     CustomElementDefinition::Id id) const {
   return id ? definitions_[id - 1].Get() : nullptr;
 }
 
 void CustomElementRegistry::AddCandidate(Element* candidate) {
-  const AtomicString& name = candidate->localName();

[dominicc (has gone to gerrit), 2017/06/26 03:03:19]

I think you should structure this differently, because <paper-button
is="dom-repeat"> should be a paper-button, not a dom-repeat. Doing it this way
makes it fragile because it subtly relies on the caller calling AddCandidate
before the attribute is set, but before the attribute is changed, and only if
the element name is not a custom element name.

I'm not confident those conditions hold.

Could you add some tests which try to mix autonomous custom elements and
is="..." attributes?

[Anton Obzhirov, 2017/06/27 19:19:00]

Yes, will do, haven’t realized you could mix both.

[Anton Obzhirov, 2017/06/28 14:09:07]

BTW according to
https://html.spec.whatwg.org/multipage/custom-elements.html#look-up-a-custom-...

7.1 If extends is a valid custom element name, then throw a "NotSupportedError"
DOMException.
So it shouldn’t be possible to extend autonomous elements via 'is' attribute.
Plz correct me if I am wrong.
In this case 'is' should always override local name. But I would say
AddCandidate should accept CustomElementDescriptor as a second parameter.

+  const AtomicString& isAttribute = candidate->getAttribute(HTMLNames::isAttr);
+  const AtomicString& name =
+      isAttribute.IsNull() ? candidate->localName() : isAttribute;
+
   if (NameIsDefined(name) || V0NameIsDefined(name))
     return;
   UpgradeCandidateMap::iterator it = upgrade_candidates_->find(name);
   UpgradeCandidateSet* set;
   if (it != upgrade_candidates_->end()) {
     set = it->value;
   } else {
     set = upgrade_candidates_->insert(name, new UpgradeCandidateSet())
               .stored_value->value;
   }
@@ skipping 35 matching lines @@
   upgrade_candidates_->erase(it);
 
   Document* document = owner_->document();
   if (!document)
     return;
 
   sorter.Sorted(elements, document);
 }
 
 }  // namespace blink