WIP static themeing

app/javascript/core/embed.js

@@ -0,0 +1,23 @@
+//  This file will be loaded on embed pages, regardless of theme.
+
+window.addEventListener('message', e => {
+  const data = e.data || {};
+
+  if (!window.parent || data.type !== 'setHeight') {
+    return;
+  }
+
+  function setEmbedHeight () {
+    window.parent.postMessage({
+      type: 'setHeight',
+      id: data.id,
+      height: document.getElementsByTagName('html')[0].scrollHeight,
+    }, '*');
+  });
+
+  if (['interactive', 'complete'].includes(document.readyState)) {
+    setEmbedHeight();
+  } else {
+    document.addEventListener('DOMContentLoaded', setEmbedHeight);
+  }
+});