custom-elements: document.createElementNS() should set prefixes to cu…

…stom elements.

We had a bug that createElementNS() ignored prefixes.
New behavior matches to the specification and Firefox.

* Document-createElementNS.html:
  Fix a copypasta error.

* ScriptCustomElementDefinition::CreateElementSync:
  Implement Step 6.1.10.

* Document::createElementNS:
  Fix an argument of definition lookup.

* CustomElement::CreateUndefinedElement:
  Use Document::CreateRawElement(), which sets prefixes correctly,
  instead of HTMLElementFactory::createHTMLElement().

* ustomElementDefinition::CreateElementAsync:
  Use Document::CreateRawElement(), which sets prefixes correctly,
  instead of HTMLElementFactory::createRawHTMLElement().

Bug: 806639
Change-Id: I74b431d4475d7cf84f65ab0ff1b24773cbc64079
Reviewed-on: https://chromium-review.googlesource.com/892802
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532821}

custom-elements/Document-createElementNS.html

@@ -28,7 +28,7 @@
 
   customElements.define('my-builtin', MyBuiltinElement, { extends: 'address' });
   let element = document.createElementNS('http://www.w3.org/1999/xhtml', 'p:address', { is: 'my-builtin'});
-  assert_true(element instanceof MyElement);
+  assert_true(element instanceof MyBuiltinElement);
   assert_equals(element.prefix, 'p');
 }, 'builtin: document.createElementNS should create custom elements with prefixes.');