title: Equivalent of ByteSize() in protobuf
body: <p>Is there an equivalent of ByteSize() for protobuf in Java? I'm trying to get the size of a protobuf before serializing it. </p>
  
  <p>Something like:</p>
  
  <pre><code>Protobuf.Builder buffer = Protobuf.newBuilder(); 
  </code></pre>
  
  <p>I need the size of the buffer now. Any idea how to obtain it?</p>