Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/aec/aec_core.cc

Index: webrtc/modules/audio_processing/aec/aec_core.cc
diff --git a/webrtc/modules/audio_processing/aec/aec_core.cc b/webrtc/modules/audio_processing/aec/aec_core.cc
index f9e96ace046ad5ab1110691c43d9d728c61a9f28..ec3feca2f1e4da2248161065f48693d908f699b3 100644
--- a/webrtc/modules/audio_processing/aec/aec_core.cc
+++ b/webrtc/modules/audio_processing/aec/aec_core.cc
@@ -201,7 +201,7 @@ void BlockBuffer::Insert(const float block[PART_LEN]) {
 }
 
 void BlockBuffer::ExtractExtendedBlock(float extended_block[PART_LEN2]) {
-  float* block_ptr = NULL;
+  float* block_ptr = nullptr;
   RTC_DCHECK_LT(0, AvaliableSpace());
 
   // Extract the previous block.
@@ -1178,7 +1178,7 @@ static void EchoSuppression(const OouraFft& ooura_fft,
   // Filter energy
   const int delayEstInterval = 10 * aec->mult;
 
-  float* xfw_ptr = NULL;
+  float* xfw_ptr = nullptr;
 
   // Update eBuf with echo subtractor output.
   memcpy(aec->eBuf + PART_LEN, echo_subtractor_output,
@@ -1467,7 +1467,7 @@ AecCore* WebRtcAec_CreateAec(int instance_count) {
   AecCore* aec = new AecCore(instance_count);
 
   if (!aec) {
-    return NULL;
+    return nullptr;
   }
   aec->nearend_buffer_size = 0;
   memset(&aec->nearend_buffer[0], 0, sizeof(aec->nearend_buffer));
@@ -1478,17 +1478,17 @@ AecCore* WebRtcAec_CreateAec(int instance_count) {
 
   aec->delay_estimator_farend =
       WebRtc_CreateDelayEstimatorFarend(PART_LEN1, kHistorySizeBlocks);
-  if (aec->delay_estimator_farend == NULL) {
+  if (aec->delay_estimator_farend == nullptr) {
     WebRtcAec_FreeAec(aec);
-    return NULL;
+    return nullptr;
   }
   // We create the delay_estimator with the same amount of maximum lookahead as
   // the delay history size (kHistorySizeBlocks) for symmetry reasons.
   aec->delay_estimator = WebRtc_CreateDelayEstimator(
       aec->delay_estimator_farend, kHistorySizeBlocks);
-  if (aec->delay_estimator == NULL) {
+  if (aec->delay_estimator == nullptr) {
     WebRtcAec_FreeAec(aec);
-    return NULL;
+    return nullptr;
   }
 #ifdef WEBRTC_ANDROID
   aec->delay_agnostic_enabled = 1;  // DA-AEC enabled by default.
@@ -1532,7 +1532,7 @@ AecCore* WebRtcAec_CreateAec(int instance_count) {
 }
 
 void WebRtcAec_FreeAec(AecCore* aec) {
-  if (aec == NULL) {
+  if (aec == nullptr) {
     return;
   }