Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc

Index: webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc
diff --git a/webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc b/webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc
index 5b0f02ef66a1fa04f645d35e7deb3be4edba778e..2421618eb3c17e66386cdbeed0448b464b20a93c 100644
--- a/webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc
+++ b/webrtc/modules/audio_coding/codecs/tools/audio_codec_speed_test.cc
@@ -34,8 +34,7 @@ AudioCodecSpeedTest::AudioCodecSpeedTest(int block_duration_ms,
       encoded_bytes_(0),
       encoding_time_ms_(0.0),
       decoding_time_ms_(0.0),
-      out_file_(NULL) {
-}
+      out_file_(nullptr) {}
 
 void AudioCodecSpeedTest::SetUp() {
   channels_ = get<0>(GetParam());
@@ -44,7 +43,7 @@ void AudioCodecSpeedTest::SetUp() {
   save_out_data_ = get<4>(GetParam());
 
   FILE* fp = fopen(in_filename_.c_str(), "rb");
-  assert(fp != NULL);
+  assert(fp != nullptr);
 
   // Obtain file size.
   fseek(fp, 0, SEEK_END);
@@ -84,7 +83,7 @@ void AudioCodecSpeedTest::SetUp() {
     out_filename = test::OutputPath() + out_filename + ".pcm";
 
     out_file_ = fopen(out_filename.c_str(), "wb");
-    assert(out_file_ != NULL);
+    assert(out_file_ != nullptr);
 
     printf("Output to be saved in %s.\n", out_filename.c_str());
   }