title: $authWithOAuthPopup() doesn't work on mobile
body: <p>The following does not open a popup/new tab/do anything on Chrome 39.0.2171.50 for iOS 8.1.2 (12B440),
   however it does seem to work on Safari on the same device:</p>
  
  <pre><code>&lt;button ng-click="$auth.$authWithOAuthPopup('facebook')"&gt;Login with Facebook&lt;/button&gt;
  </code></pre>
  
  <p>See plnkr: <a href="http://plnkr.co/edit/Ejd7fsyTHf6Ohn0F25Wy?p=preview">http://plnkr.co/edit/Ejd7fsyTHf6Ohn0F25Wy?p=preview</a></p>
  
  <p>Is this a bug with Chrome or Firebase/AngularFire or am I doing something incorrectly?</p>
  
  <p>I see from <a href="https://groups.google.com/forum/#!topic/firebase-talk/8vwtH1P9l_w">here</a> that this may be a Chrome issue, however I can't get <code>$authWithOAuthRedirect()</code> to work either; see: <a href="http://plnkr.co/edit/9dd0W8X5k33LFBcCLmzs?p=preview">http://plnkr.co/edit/9dd0W8X5k33LFBcCLmzs?p=preview</a></p>
  
  <p>Both Popup and Redirect work on Desktop Chrome 39.0.2171.95</p>