Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/dtmf_tone_generator_unittest.cc

 /*
  *  Copyright (c) 2012 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 153 matching lines @@
             tone_gen.Init(fs, 16, attenuation));
   // Initialize with invalid attenuation -1.
   EXPECT_EQ(DtmfToneGenerator::kParameterError, tone_gen.Init(fs, event, -1));
   // Initialize with invalid attenuation 64.
   EXPECT_EQ(DtmfToneGenerator::kParameterError, tone_gen.Init(fs, event, 64));
   EXPECT_FALSE(tone_gen.initialized());  // Should still be uninitialized.
 
   // Initialize with valid parameters.
   ASSERT_EQ(0, tone_gen.Init(fs, event, attenuation));
   EXPECT_TRUE(tone_gen.initialized());
-  // NULL pointer to destination.
+  // null pointer to destination.
   EXPECT_EQ(DtmfToneGenerator::kParameterError,
-            tone_gen.Generate(kNumSamples, NULL));
+            tone_gen.Generate(kNumSamples, nullptr));
 }
 
 }  // namespace webrtc