The top-level message sent by the client for the
StreamingRecognize method. Multiple StreamingRecognizeRequest
messages are sent. The first message must contain a streaming_config
message and must not contain audio_content. All subsequent messages
must contain audio_content and must not contain a
streaming_config message.
Provides information to the recognizer that specifies how to
process the request. The first StreamingRecognizeRequest
message must contain a streaming_config message.