Merge pull request #3241 from daspecster/speech-add-result-index

Add docs for 'result_index'  usage and a system test.

Author: daspecster

google-cloud-speech/tests/system.py

@@ -200,6 +200,7 @@ def test_stream_recognize(self):
 
         with open(AUDIO_FILE, 'rb') as file_obj:
             for results in self._make_streaming_request(file_obj):
+                self.assertIsInstance(results.result_index, int)
                 self._check_results(results.alternatives)
 
     def test_stream_recognize_interim_results(self):