title: Polymer paper tabs not rendering properly
body: <p>I have just been learning polymer and have been following the tutorial in this website: polymer-project.org</p>
  
  <p>I am at the part where I am to place paper tabs on the core-header-panel. Following the tutorial, I am not able to render the paper tabs completely. But if I remove the core-header-panel and core-toolbar tags, I was able to render them.</p>
  
  <p>Here's the code that doesn't render the tabs:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;&lt;/title&gt;
      &lt;script src="bower_components/platform/platform.js" &gt;&lt;/script&gt;
      &lt;link rel="import" href="bower_components/polymer/polymer.html"&gt;
      &lt;link rel="import" href="bower_components/font-roboto/roboto.html"&gt;
      &lt;link rel="import" href="bower_components/core-header-panel/core-header-panel.html"&gt;
      &lt;link rel="import" href="bower_components/core-toolbar/core-toolbar.html"&gt;
      &lt;link rel="import" href="bower_components/paper-tabs/paper-tabs.html"&gt;
  &lt;/head&gt;
  
  &lt;body unresolved touch-action="auto"&gt;
      &lt;core-header-panel&gt;
          &lt;core-toolbar&gt;
              &lt;paper-tabs valueattr="name" selected="all" self-end&gt;
                  &lt;paper-tab name="all"&gt;All&lt;/paper-tab&gt;
                  &lt;paper-tab name="favorites"&gt;FAVORITES&lt;/paper-tab&gt;
              &lt;/paper-tabs&gt;
          &lt;/core-toolbar&gt;
      &lt;/core-header-panel&gt;
  &lt;script&gt;
      var tabs = document.querySelector('paper-tabs');
      tabs.addEventListener('core-select', function(){
          console.log("Selected: " + tabs.selected);
      });
  &lt;/script&gt;
  
  &lt;/body&gt;
  </code></pre>
  
  <p>And here's the code that renders the tabs:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;&lt;/title&gt;
      &lt;script src="bower_components/platform/platform.js" &gt;&lt;/script&gt;
      &lt;link rel="import" href="bower_components/polymer/polymer.html"&gt;
      &lt;link rel="import" href="bower_components/font-roboto/roboto.html"&gt;
      &lt;link rel="import" href="bower_components/core-header-panel/core-header-panel.html"&gt;
      &lt;link rel="import" href="bower_components/core-toolbar/core-toolbar.html"&gt;
      &lt;link rel="import" href="bower_components/paper-tabs/paper-tabs.html"&gt;
  &lt;/head&gt;
  
  &lt;body unresolved touch-action="auto"&gt;
  
              &lt;paper-tabs valueattr="name" selected="all" self-end&gt;
                  &lt;paper-tab name="all"&gt;All&lt;/paper-tab&gt;
                  &lt;paper-tab name="favorites"&gt;FAVORITES&lt;/paper-tab&gt;
              &lt;/paper-tabs&gt;
  
  &lt;script&gt;
      var tabs = document.querySelector('paper-tabs');
      tabs.addEventListener('core-select', function(){
          console.log("Selected: " + tabs.selected);
      });
  &lt;/script&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>