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.cc b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
index b8e8c71..15eb51b 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.cc
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
@@ -35,7 +35,7 @@
 #include "webrtc/modules/audio_coding/neteq/dtmf_tone_generator.h"
 #include "webrtc/modules/audio_coding/neteq/expand.h"
 #include "webrtc/modules/audio_coding/neteq/merge.h"
-#include "webrtc/modules/audio_coding/neteq/nack.h"
+#include "webrtc/modules/audio_coding/neteq/nack_tracker.h"
 #include "webrtc/modules/audio_coding/neteq/normal.h"
 #include "webrtc/modules/audio_coding/neteq/packet_buffer.h"
 #include "webrtc/modules/audio_coding/neteq/packet.h"
@@ -476,7 +476,7 @@
   rtc::CritScope lock(&crit_sect_);
   if (!nack_enabled_) {
     const int kNackThresholdPackets = 2;
-    nack_.reset(Nack::Create(kNackThresholdPackets));
+    nack_.reset(NackTracker::Create(kNackThresholdPackets));
     nack_enabled_ = true;
     nack_->UpdateSampleRate(fs_hz_);
   }