title: Counter not available with custom trace
body: <p>I'm using <code>Firebase Performance Monitoring</code> plug-in for my projects, in order to track / inspect my code.</p>
  
  <p>I create a <code>Trace</code> on the <code>onPreExecute()</code> method of custom <code>AsyncTask</code> (here I post only the methods where I use <code>Trace</code>) : </p>
  
  <pre><code>@Override
  protected void onPreExecute() {
      // Start trace which track the analysis of raw data
      Trace trace = FirebasePerformance.getInstance().newTrace(traceTag);
      mTraceMaps.put(traceTag, trace);
      trace.start();
      trace.incrementCounter(counterTag, totalItems);
  }
  
  @Override
  protected void onPostExecute(Bundle result) {
      // Stop trace which track the analysis of raw data
      Trace trace = mTraceMaps.get(traceTag);
      if (trace != null) {
          trace.stop();
          mTraceMaps.remove(traceTag);
      }
  }
  </code></pre>
  
  <p>Please note that <code>traceTag</code> and <code>counterTag</code> are constants in my class.</p>
  
  <p>The problem is that I can't see anything on <strong>Firebase console</strong>. I'm expecting an <code>int</code> showing me how many raw data I collected.</p>
  
  <p>Am I missing something ? Does my code is correct ?</p>