Fix upgrading built-in custom elements

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

Index: third_party/WebKit/Source/core/dom/custom/CustomElementRegistry.cpp
diff --git a/third_party/WebKit/Source/core/dom/custom/CustomElementRegistry.cpp b/third_party/WebKit/Source/core/dom/custom/CustomElementRegistry.cpp
index ea2454774c2b87e9ac443db58d284cb2dde73364..c7b1d7490315e9a26c1f69190785897656871bfb 100644
--- a/third_party/WebKit/Source/core/dom/custom/CustomElementRegistry.cpp
+++ b/third_party/WebKit/Source/core/dom/custom/CustomElementRegistry.cpp
@@ -270,7 +270,10 @@ CustomElementDefinition* CustomElementRegistry::DefinitionForId(
 }
 
 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);