title: Using <template is="dom-if" with a condition
body: <p>I have a <code>&lt;template is="dom-if" if=...</code> that I want to use with a logical condition.</p>
  
  <p>Any binding I try appears to be <em>truthy</em>:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;link href="https://polygit.org/components/polymer/polymer.html" rel="import"&gt;
  
  &lt;dom-module id="test-thing"&gt;
    &lt;template&gt;
      &lt;template is="dom-if" if="{{title == 'foo'}}" restamp&gt;
        Title is &lt;b&gt;FOO&lt;/b&gt;
      &lt;/template&gt;
      &lt;template is="dom-if" if="{{title}} == 'bar'" restamp&gt;
        Title is &lt;b&gt;BAR&lt;/b&gt;
      &lt;/template&gt;
      
      Actual: "{{title}}"
    &lt;/template&gt;
    &lt;script&gt;
      Polymer({
        is: 'test-thing',
        properties: {
          title: {type: String,value:''}
        }
      });
    &lt;/script&gt;
  &lt;/dom-module&gt;
  
  &lt;div&gt;
    Title: foo&lt;br&gt;
    &lt;test-thing title="foo"&gt;&lt;/test-thing&gt;
  &lt;/div&gt;
  &lt;div&gt;
    Title: bar&lt;br&gt;
    &lt;test-thing title="bar"&gt;&lt;/test-thing&gt;
  &lt;/div&gt;
  &lt;div&gt;
    Title: abc&lt;br&gt;
    &lt;test-thing title="abc"&gt;&lt;/test-thing&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>What is the correct way to apply an <code>if</code> condition to a <code>dom-if</code> <code>template</code>?</p>