Replace NULL with nullptr or null in webrtc/audio/ and common_audio/.

webrtc/common_audio/signal_processing/real_fft_unittest.cc

Index: webrtc/common_audio/signal_processing/real_fft_unittest.cc
diff --git a/webrtc/common_audio/signal_processing/real_fft_unittest.cc b/webrtc/common_audio/signal_processing/real_fft_unittest.cc
index 8b1c4310787d19c06a08e7a16a640872180a043b..282342230f278830be701c41927e5db5dbdcaabb 100644
--- a/webrtc/common_audio/signal_processing/real_fft_unittest.cc
+++ b/webrtc/common_audio/signal_processing/real_fft_unittest.cc
@@ -42,9 +42,9 @@ class RealFFTTest : public ::testing::Test {
 
 TEST_F(RealFFTTest, CreateFailsOnBadInput) {
   RealFFT* fft = WebRtcSpl_CreateRealFFT(11);
-  EXPECT_TRUE(fft == NULL);
+  EXPECT_TRUE(fft == nullptr);
   fft = WebRtcSpl_CreateRealFFT(-1);
-  EXPECT_TRUE(fft == NULL);
+  EXPECT_TRUE(fft == nullptr);
 }
 
 TEST_F(RealFFTTest, RealAndComplexMatch) {
@@ -64,7 +64,7 @@ TEST_F(RealFFTTest, RealAndComplexMatch) {
 
   // Create and run real forward FFT.
   RealFFT* fft = WebRtcSpl_CreateRealFFT(kOrder);
-  EXPECT_TRUE(fft != NULL);
+  EXPECT_TRUE(fft != nullptr);
   EXPECT_EQ(0, WebRtcSpl_RealForwardFFT(fft, real_fft_time, real_fft_freq));
 
   // Run complex forward FFT.