Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc

Index: webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc
diff --git a/webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc b/webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc
index 65b516a7c53c5ecec24ebe12dcbf27228dc02e59..68694946c3804016cf0c455e594030515936e9cc 100644
--- a/webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc
+++ b/webrtc/modules/audio_processing/vad/vad_audio_proc_unittest.cc
@@ -32,12 +32,12 @@ TEST(AudioProcessingTest, DISABLED_ComputingFirstSpectralPeak) {
   std::string peak_file_name =
       test::ResourcePath("audio_processing/agc/agc_spectral_peak", "dat");
   FILE* peak_file = fopen(peak_file_name.c_str(), "rb");
-  ASSERT_TRUE(peak_file != NULL);
+  ASSERT_TRUE(peak_file != nullptr);
 
   std::string pcm_file_name =
       test::ResourcePath("audio_processing/agc/agc_audio", "pcm");
   FILE* pcm_file = fopen(pcm_file_name.c_str(), "rb");
-  ASSERT_TRUE(pcm_file != NULL);
+  ASSERT_TRUE(pcm_file != nullptr);
 
   // Read 10 ms audio in each iteration.
   const size_t kDataLength = kLength10Ms;