Adding a delay line to NetEq's output

This change adds an optional delay to NetEq's output. Note, this is not
equivalent to increasing the jitter buffer with the same extra length.

Bug: b/156734419
Change-Id: I8b70b6b3bffcfd3da296ccf29853864baa03d6bb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175110
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31343}
diff --git a/api/audio/audio_frame.h b/api/audio/audio_frame.h
index 06b0b28..78539f5 100644
--- a/api/audio/audio_frame.h
+++ b/api/audio/audio_frame.h
@@ -14,6 +14,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <utility>
+
 #include "api/audio/channel_layout.h"
 #include "api/rtp_packet_infos.h"
 #include "rtc_base/constructor_magic.h"
@@ -58,6 +60,8 @@
 
   AudioFrame();
 
+  friend void swap(AudioFrame& a, AudioFrame& b);
+
   // Resets all members to their default state.
   void Reset();
   // Same as Reset(), but leaves mute state unchanged. Muting a frame requires