Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/echo_cancellation_impl.cc

Index: webrtc/modules/audio_processing/echo_cancellation_impl.cc
diff --git a/webrtc/modules/audio_processing/echo_cancellation_impl.cc b/webrtc/modules/audio_processing/echo_cancellation_impl.cc
index 9918bb473859349362db621ac8cc0ce603723bca..333689a953409b649eddf7668be442571b38beb3 100644
--- a/webrtc/modules/audio_processing/echo_cancellation_impl.cc
+++ b/webrtc/modules/audio_processing/echo_cancellation_impl.cc
@@ -44,7 +44,7 @@ AudioProcessing::Error MapError(int err) {
     default:
       // AEC_UNSPECIFIED_ERROR
       // AEC_UNINITIALIZED_ERROR
-      // AEC_NULL_POINTER_ERROR
+      // AEC_null_POINTER_ERROR
       return AudioProcessing::kUnspecifiedError;
   }
 }
@@ -276,7 +276,7 @@ bool EchoCancellationImpl::are_metrics_enabled() const {
 //            aboue the best way to extend this to multi-channel.
 int EchoCancellationImpl::GetMetrics(Metrics* metrics) {
   rtc::CritScope cs(crit_capture_);
-  if (metrics == NULL) {
+  if (metrics == nullptr) {
     return AudioProcessing::kNullPointerError;
   }
 
@@ -365,10 +365,10 @@ int EchoCancellationImpl::GetDelayMetrics(int* median, int* std) {
 int EchoCancellationImpl::GetDelayMetrics(int* median, int* std,
                                           float* fraction_poor_delays) {
   rtc::CritScope cs(crit_capture_);
-  if (median == NULL) {
+  if (median == nullptr) {
     return AudioProcessing::kNullPointerError;
   }
-  if (std == NULL) {
+  if (std == nullptr) {
     return AudioProcessing::kNullPointerError;
   }
 
@@ -388,7 +388,7 @@ int EchoCancellationImpl::GetDelayMetrics(int* median, int* std,
 struct AecCore* EchoCancellationImpl::aec_core() const {
   rtc::CritScope cs(crit_capture_);
   if (!enabled_) {
-    return NULL;
+    return nullptr;
   }
   return WebRtcAec_aec_core(cancellers_[0]->state());
 }