NetEq: Rename Nack to NackTracker to avoid name collisions in GN

BUG=webrtc:5949
NOTRY=True
R=kjellander@webrtc.org

Review-Url: https://codereview.webrtc.org/2045243002
Cr-Commit-Position: refs/heads/master@{#13069}
diff --git a/webrtc/modules/audio_coding/neteq/neteq_impl.h b/webrtc/modules/audio_coding/neteq/neteq_impl.h
index 58b705b..2b10f97 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.h
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.h
@@ -42,7 +42,7 @@
 class DtmfToneGenerator;
 class Expand;
 class Merge;
-class Nack;
+class NackTracker;
 class Normal;
 class PacketBuffer;
 class PayloadSplitter;
@@ -405,7 +405,7 @@
   const BackgroundNoiseMode background_noise_mode_ GUARDED_BY(crit_sect_);
   NetEqPlayoutMode playout_mode_ GUARDED_BY(crit_sect_);
   bool enable_fast_accelerate_ GUARDED_BY(crit_sect_);
-  std::unique_ptr<Nack> nack_ GUARDED_BY(crit_sect_);
+  std::unique_ptr<NackTracker> nack_ GUARDED_BY(crit_sect_);
   bool nack_enabled_ GUARDED_BY(crit_sect_);
   const bool enable_muted_state_ GUARDED_BY(crit_sect_);
   AudioFrame::VADActivity last_vad_activity_ GUARDED_BY(crit_sect_) =