Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/test/utility.cc

Index: webrtc/modules/audio_coding/test/utility.cc
diff --git a/webrtc/modules/audio_coding/test/utility.cc b/webrtc/modules/audio_coding/test/utility.cc
index 5c1fc3f968dc7e81af8fab9c954609a3794f533f..8caf927b68b7e21a7a6699402833bf180a6b0613 100644
--- a/webrtc/modules/audio_coding/test/utility.cc
+++ b/webrtc/modules/audio_coding/test/utility.cc
@@ -111,7 +111,7 @@ int16_t ChooseCodec(CodecInst& codecInst) {
   char myStr[15] = "";
   do {
     printf("\nChoose a codec [0]: ");
-    EXPECT_TRUE(fgets(myStr, 10, stdin) != NULL);
+    EXPECT_TRUE(fgets(myStr, 10, stdin) != nullptr);
     codecID = atoi(myStr);
     if ((codecID < 0) || (codecID >= noCodec)) {
       printf("\nOut of range.\n");
@@ -137,7 +137,7 @@ void PrintCodecs() {
 }
 
 CircularBuffer::CircularBuffer(uint32_t len)
-    : _buff(NULL),
+    : _buff(nullptr),
       _idx(0),
       _buffIsFull(false),
       _calcAvg(false),
@@ -145,7 +145,7 @@ CircularBuffer::CircularBuffer(uint32_t len)
       _sum(0),
       _sumSqr(0) {
   _buff = new double[len];
-  if (_buff == NULL) {
+  if (_buff == nullptr) {
     _buffLen = 0;
   } else {
     for (uint32_t n = 0; n < len; n++) {
@@ -156,9 +156,9 @@ CircularBuffer::CircularBuffer(uint32_t len)
 }
 
 CircularBuffer::~CircularBuffer() {
-  if (_buff != NULL) {
+  if (_buff != nullptr) {
     delete[] _buff;
-    _buff = NULL;
+    _buff = nullptr;
   }
 }