title: LiveDataReactiveStreams: converting Flowable to LiveData doesn't work
body: <p>I'm trying to convert a Flowable into LiveData and observing it in the activity. My Flowable is emitting values with a constant delay ,
  but the LiveData which i'm converting this Flowable to, is not at all receiving any values in its observer. I have created a sample code to 
  demonstrate the problem </p>
  
  <p>Activity </p>
  
  <pre><code>    public class MyrActivity extends AppCompatActivity {
  
          @Override
          protected void onCreate(Bundle savedInstanceState) {
              super.onCreate(savedInstanceState);
              setContentView(R.layout.activity_my);
              MyViewModel myViewModel = ViewModelProviders.of(this).get(MyViewModel.class);
              myViewModel.init();
              myViewModel.getListLiveData().observe(this, new Observer&lt;List&lt;String&gt;&gt;() {
                  @Override
                  public void onChanged(@Nullable List&lt;String&gt; strings) {
                      Timber.d("value received in live data observer: %s", strings);
                      // This callback never get called
                      for (String string : strings) {
                          Timber.d(string);
                      }
                  }
              });
  
          }
      }
  </code></pre>
  
  <p>ViewModel  class</p>
  
  <pre><code>     static class MyViewModel extends ViewModel{
              LiveData&lt;List&lt;String&gt;&gt; mListLiveData;
              PublishProcessor&lt;String&gt; mStringPublishProcessor = PublishProcessor.create();
  
              public void init() {
                  mListLiveData = LiveDataReactiveStreams.fromPublisher(mStringPublishProcessor.toList().toFlowable());
  
                  // This is to trigger the mStringPublishProcessor on constant intervals
                  Observable.interval(0,5,TimeUnit.SECONDS)
                          .map(aLong -&gt; {
                              Timber.d("value emitted: ");  // this log is showing as expected
                              mStringPublishProcessor.onNext("Value "+aLong);
                              return aLong;
                          }).subscribe();
              }
  
              public LiveData&lt;List&lt;String&gt;&gt; getListLiveData() {
                  return mListLiveData;
              }
          }
  </code></pre>
  
  <p>Now , in my activity I can see only the logs from the <code>Observable.interval</code></p>
  
  <pre><code>     com.example.app D/MyActivity$MyViewModel: value emitted: 
       com.example.app D/MyActivity$MyViewModel: value emitted: 
       com.example.app D/MyActivity$MyViewModel: value emitted: 
       com.example.app D/MyActivity$MyViewModel: value emitted: 
       com.example.app D/MyActivity$MyViewModel: value emitted: 
       com.example.app D/MyActivity$MyViewModel: value emitted: 
  </code></pre>
  
  <p>Why the LiveData observer never received any values from the Flowable?</p>
  
  <p>as per the documentation of LiveDataReactiveStreams.fromPublisher</p>
  
  <blockquote>
    <p>Creates an Observable stream from a ReactiveStreams publisher.
         When the LiveData becomes active, it subscribes to the emissions from the Publisher.</p>
  </blockquote>