Embed DartPad in the top part of homepage

src/tests/site/gists/homepage_jw_html/web/main.dart

+import 'dart:html';
+
+main() async {
+  const findMe = 'jabberwock';
+
+  // Find an element with the ID "jw".
+  var displayer = querySelector('#jw');
+
+  // Get the text to display, and display it.
+  var lines = await getLines(findMe);
+  lines?.forEach((line) {
+    print(line);
+    displayer?.text += line + '\n';
+  });
+
+  // Find all elements with the class "searchString".
+  querySelectorAll('.searchString').forEach((el) {
+    // Set each one's text and highlight it.
+    el..text = findMe
+      ..classes.add('highlighted');
+  });
+}
+
+// Reads a file, returning its lines.
+getLines(String withString) async {
+  var jabber = await HttpRequest.getString(
+      'https://www.dartlang.org/samples-files/jabberwocky.txt');
+  var lines = jabber.split('\n');
+  lines.retainWhere((line) =>
+      line.toLowerCase().contains(withString));
+  return lines;
+}