Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/codecs/red/audio_encoder_copy_red_unittest.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 35 matching lines @@
     EXPECT_CALL(*mock_encoder_, SampleRateHz())
         .WillRepeatedly(Return(sample_rate_hz_));
   }
 
   void TearDown() override {
     EXPECT_CALL(*mock_encoder_, Die()).Times(1);
     red_.reset();
   }
 
   void Encode() {
-    ASSERT_TRUE(red_.get() != NULL);
+    ASSERT_TRUE(red_.get() != nullptr);
     encoded_.Clear();
     encoded_info_ = red_->Encode(
         timestamp_,
         rtc::ArrayView<const int16_t>(audio_, num_audio_samples_10ms),
         &encoded_);
     timestamp_ += num_audio_samples_10ms;
   }
 
   MockAudioEncoder* mock_encoder_;
   std::unique_ptr<AudioEncoderCopyRed> red_;
@@ skipping 219 matching lines @@
 };
 
 TEST_F(AudioEncoderCopyRedDeathTest, WrongFrameSize) {
   num_audio_samples_10ms *= 2;  // 20 ms frame.
   EXPECT_DEATH(Encode(), "");
   num_audio_samples_10ms = 0;  // Zero samples.
   EXPECT_DEATH(Encode(), "");
 }
 
 TEST_F(AudioEncoderCopyRedDeathTest, NullSpeechEncoder) {
-  AudioEncoderCopyRed* red = NULL;
+  AudioEncoderCopyRed* red = nullptr;
   AudioEncoderCopyRed::Config config;
-  config.speech_encoder = NULL;
+  config.speech_encoder = nullptr;
   EXPECT_DEATH(red = new AudioEncoderCopyRed(std::move(config)),
                "Speech encoder not provided.");
   // The delete operation is needed to avoid leak reports from memcheck.
   delete red;
 }
 
 #endif  // GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
 
 }  // namespace webrtc