Embed DartPad in the top part of homepage

src/site/index.html

 ---
 layout: homepage
+js:
+- url: /js/carousel-next.js
+  defer: true
 ---
 
   <div class="container-page">
     <div class="container-full hero-hldr">
-      <div class="hero container">
-        <div class="row">
-          <div class="col-md-10 col-md-offset-1">
-            <h1>Scalable, productive app development</h1>
-                    <p>
-              Dart is an open-source, scalable programming language, with
-              robust libraries and runtimes, for building web, server, and
-              mobile apps.
-                    </p>
-              {% include downloads/_dart.html buttonclass="btn-default" %}
+      <div id="top-carousel" class="carousel slide dart-carousel" data-interval="false">
+
+        <!-- Indicators -->
+        <ol class="carousel-indicators">
+          <li data-target="#top-carousel" data-slide-to="0" class="active">Welcome to Dart!</li>
+          <li data-target="#top-carousel" data-slide-to="1">Try Dart</li>
+        </ol>
+
+        <!-- Wrapper for slides -->
+        <div class="carousel-inner" height="500px">
+
+          <!-- SLIDE 1: original hero content -->
+          <div class="item active">
+            <div class="hero container">
+              <div class="row">
+                <div class="col-md-10 col-md-offset-1">
+                  <h1>Scalable, productive app development</h1>
+                    <p>
+                    Dart is an open-source, scalable programming language, with
+                    robust libraries and runtimes, for building web, server, and
+                    mobile apps.
+                    </p>
+
+                    <button class="btn btn-lg try-btn" id="carousel-next">
+                      Try Dart
+                    </button>
+
+                    <div class="editor-current-version version">
+                      Current stable version of Dart:
+                      <span class="editor-build-rev-stable">[calculating]</span>
+                    </div>
+                </div>
+              </div>
+            </div>
+            <div class="container-full sub-hero-hldr">
+              <div id="feed-posts" class="sub-hero container">
+              </div>
+            </div>
           </div>
-        </div>
-      </div>
-    </div>
 
-    <div class="container-full sub-hero-hldr">
-      <div id="feed-posts" class="sub-hero container">
-      </div>
-    </div>
+          <!-- SLIDE 2: dartpad -->
+          <div class="item code-hldr" style="padding-top: 24px; height: 460px">
+            {% comment %}
+            https://dartpad.dartlang.org/a6907e26b96678b75303
+            https://gist.github.com/a6907e26b96678b75303
+            verticalRatio set to a value that makes output have no scrollbar.
+            {% endcomment %}
+            <iframe src="{{site.custom.dartpad.embed-dart-prefix}}?id=a6907e26b96678b75303&verticalRatio=73"
+                    width="100%" height="100%"
+                    style="border: 1px solid #ccc;"></iframe>
+          </div>
+        </div> <!-- END slides -->
+      </div> <!-- END carousel -->
+    </div> <!-- END hero -->
 
     <div class="container dart-container">
-
       <section class="dart-ctas">
         <div class="row">
           <div class="col-md-10 col-md-offset-1">
             <div class="row">
               <div class="col-md-4">
                 <h2>
                   <a id="see-code" href="#code" data-slide="true">See Dart</a>
                 </h2>
                 <p class="timer"><i class="sprite-icon-timer"></i>About 5 minutes</p>
                 <p>Dart is class based and object oriented, without being dogmatic.</p>
@@ skipping 365 matching lines @@
         <div class="row">
           <div class="col-md-12" id="tools">
             <h2>Dart’s tools help you be productive</h2>
             <p>
               With <a href="https://dartpad.dartlang.org">DartPad</a>,
               you can write and run simple Dart programs in your browser.
               Once you're ready to get serious, use whichever IDE or editor you like.
               <a href="/tools/">Dart plugins</a> exist for WebStorm, Eclipse,
               Sublime Text, and more.
             </p>
+
             <a href="https://dartpad.dartlang.org"><img src="imgs/dartpad.png" alt="screenshot of DartPad"
                 style="margin-bottom:0px"></a>
           </div>
         </div>
         <div class="row productivity-tools-options">
           <div class="row">
             <div class="col-md-4 col-md-offset-2">
               <h4><a href="/tools/pub/">Pub package manager</a></h4>
               <p>The easiest way to get and share Dart code, pub keeps your packages up to date, handling versioning and dependency.</p>
             </div>
@@ skipping 21 matching lines @@
           <aside class="alert alert-info os-choices col-md-8 col-md-offset-2">
             <b>Note:</b>
             You can write Dart apps using any recent version of
             Windows, Linux, or Mac.
             The Dart development tools <b>do not&nbsp;support Windows XP</b>.
           </aside>
         </div>
       </section>
     </div> <!-- end container -->
   </div> <!-- end container-page -->