Make custom elements work in HTML imports

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

Index: third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp
diff --git a/third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp b/third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp
index a9e7d5cd80b3ae9db6a1ff58feab377d277472db..db82d7bbadc7ea20a9d938449f7c0f39c7d5e6be 100644
--- a/third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp
+++ b/third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp
@@ -55,8 +55,10 @@ static String errorMessageForConstructorResult(Element* element,
     if (element->parentNode())
         return "The result must not have a parent";
     // 6.1.7. If result's node document is not document, then throw a NotSupportedError.
-    if (&element->document() != &document)
+    if (&element->document() != &document
+        && element->document().contextDocument() != document.contextDocument()) {

[dominicc (has gone to gerrit), 2016/08/19 04:54:11]

I'm not sure this is right. Why would we disallow moving from the main document,
to an unrelated document, but allow moving from one import to another import?

[kochi, 2016/08/22 07:37:34]

I'm not sure I understand "unrelated document" here.

My understanding is that, custom element definition is
always on window.customElements (registry), and both document.createElement()
and importDocument.createElement() should work.

         return "The result must be in the same document";
+    }
     // 6.1.8. If result's namespace is not the HTML namespace, then throw a NotSupportedError.
     if (element->namespaceURI() != HTMLNames::xhtmlNamespaceURI)
         return "The result must have HTML namespace";