title: Can't get a list of cast devices on the network
body: <p>I'm trying to get a list of cast devices programmatically in Android, without using the MediaRouteActionProvider button in the SDK.  </p>
  
  <p>I create a MediaRouter and MediaRouteSelector like so:</p>
  
  <pre><code>mMediaRouter = MediaRouter.getInstance(this);
  mMediaRouteSelector = new MediaRouteSelector.Builder()
     .addControlCategory(CastMediaControlIntent.CATEGORY_CAST)
     .build();
  </code></pre>
  
  <p>I then start discovery:</p>
  
  <pre><code>mMediaRouter.addCallback(mMediaRouteSelector, mMediaRouterCallback,
     MediaRouter.CALLBACK_FLAG_PERFORM_ACTIVE_SCAN);
  </code></pre>
  
  <p>In the onProviderAdded callback method, I only seem to get 3 providers: Android, com.google.android.youtube, and com.google.android.gms.  Only 'android' provides a route, which is named 'Phone'.</p>
  
  <p>Why isn't my chromecast device showing up?  Other apps can see it, so I should have connectivity.</p>