Change NetEq::GetPlayoutTimestamp to return an rtc::Optional<uint32_t>

webrtc/modules/audio_coding/acm2/acm_receiver.h

Index: webrtc/modules/audio_coding/acm2/acm_receiver.h
diff --git a/webrtc/modules/audio_coding/acm2/acm_receiver.h b/webrtc/modules/audio_coding/acm2/acm_receiver.h
index 77eb563972377197c5d61c635248e04db209c4a1..6fec1ffdda1f965ed94f3cb8bbd6114755bfa2ed 100644
--- a/webrtc/modules/audio_coding/acm2/acm_receiver.h
+++ b/webrtc/modules/audio_coding/acm2/acm_receiver.h
@@ -195,11 +195,9 @@ class AcmReceiver {
   //
   int RemoveAllCodecs();
 
-  //
-  // Gets the RTP timestamp of the last sample delivered by GetAudio().
-  // Returns true if the RTP timestamp is valid, otherwise false.
-  //
-  bool GetPlayoutTimestamp(uint32_t* timestamp);
+  // Returns the RTP timestamp for the last sample delivered by GetAudio().
+  // The return value will be empty if no valid timestamp is available.
+  rtc::Optional<uint32_t> GetPlayoutTimestamp();
 
   //
   // Get the audio codec associated with the last non-CNG/non-DTMF received