title: UICollectionView not calling intrinsicContentSize
body: <p>I have a <code>UICollectionViewController</code> which generates cells with a random color for testing purposes. Now that the <code>UICollectionViewController</code> is embedded in a <code>UIScrollView</code>, I want the scrollView to be the same size as it's <code>contentSize</code>. </p>
  
  <p>I made a subclass of <code>UICollectionView</code>, implemented <code>intrinsicContentSize</code> method, and set the <code>UICollectionView</code>'s class to my custom class in IB. However <code>intrinsicContentSize</code> never gets called. I have the exact same setup with an <code>UITableView</code> and there it works flawlessly.</p>
  
  <p>Any ideas on this?</p>
  
  <pre class="lang-c prettyprint-override"><code>- (CGSize)intrinsicContentSize {
      [self layoutIfNeeded];
      return CGSizeMake(UIViewNoIntrinsicMetric, self.contentSize.height);
  }
  </code></pre>