Add a basic SkyBinder test.

sky/framework/dom-serializer.sky

Index: sky/framework/dom-serializer.sky
diff --git a/sky/framework/dom-serializer.sky b/sky/framework/dom-serializer.sky
index ac352fffde8717906586cc9ebcd1302bbed7d9f2..e32b88fedddd6fb8a8149a607bb49591104bb5cf 100644
--- a/sky/framework/dom-serializer.sky
+++ b/sky/framework/dom-serializer.sky
@@ -63,7 +63,7 @@ function serializeNode(node) {
     return escapeText(node.data, kTextEscapePattern);
   if (node instanceof Element)
     return serializeElement(node);
-  if (node instanceof Document)
+  if (node instanceof Document || node instanceof ShadowRoot)
     return serializeChildren(node.firstChild);
   throw new Error("Cannot serialize node");
 }