added front page samples to testing, plus a couple of tweaks to front page and code lab

src/tests/site/code/htmllib.dart

+import 'dart:html';
+import 'dart:convert' show JSON;
+
+void main() {
+  querySelector('#getColors').onClick.listen(showColors); // Event handling.
+}
+void showColors(Event e) {
+  HttpRequest.getString('colors.json')             // One-line HTTP request.
+      .then((String jsonString) {                   // Uses Futures and Streams.
+        UListElement colors = querySelector('#colors');  // DOM element types.
+        List colorList = JSON.decode(jsonString);
+        for (int i = 0; i < colorList.length; i++) {
+          colors.children.add(                      // Dynamic DOM manipulation.
+            new LIElement()..text = colorList[i]    // Dynamic element creation.
+             ..style.color = colorList[i]           // Uniform CSS styles.
+             ..style.fontFamily = 'Marker Felt');
+        }
+      })
+      .catchError((_) { /* Handle error. */ });
+}