Make custom elements work in HTML imports

third_party/WebKit/LayoutTests/custom-elements/imports/resources/create-element.html

+<div id="sandbox"></div>
+<script>
+test(() => {
+  assert_equals(constructors.length, 0);
+
+  class CreateElement extends HTMLElement {

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

Give this a different name; calling it CreateElement is a bit confusing because
there's a method called createElement.

[kochi, 2016/08/19 10:51:48]

Done.

+    constructor() {
+      super();
+      constructors.push('constructor');
+    }
+  }
+
+  customElements.define('create-element', CreateElement);

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

We've generally used a-a for a succinct custom element name.

[kochi, 2016/08/19 10:51:48]

Done.

+
+  let importDoc = document.currentScript.ownerDocument;
+  let sandbox = importDoc.querySelector('#sandbox');
+
+  // createElement should synchronously customize.

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

Maybe delete the blank line between createElement and the assertion. This
comment more pertains to what you're asserting, so put them together with
createElement as the meat in the sandwich.

[kochi, 2016/08/19 10:51:48]

Done.

+  let el = document.createElement('create-element');
+
+  assert_equals(constructors.length, 1);
+
+  let el2 = new CreateElement();
+
+  sandbox.appendChild(el);
+  sandbox.appendChild(el2);
+
+  // TODO: test something

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

Be more specific: TODO(who): what when

[kochi, 2016/08/19 10:51:48]

Yeah, this test was very work in progress...
This was a reminder for myself :)

+
+}, 'createElement() should work in imported document.');

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

Add assertions for importDoc.createElement. What semantics do you want that to
have?

[kochi, 2016/08/19 10:51:48]

Done.

+</script>