Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc

Index: webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc
diff --git a/webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc b/webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc
index 1ee92a11c576d8f85c76d46428f37e8e8237030d..0aa16b4a5eb57099cb3e6bd9895922f97d0a11d9 100644
--- a/webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc
+++ b/webrtc/modules/audio_coding/neteq/audio_decoder_unittest.cc
@@ -100,7 +100,7 @@ class AudioDecoderTest : public ::testing::Test {
         data_length_(0),
         channels_(1),
         payload_type_(17),
-        decoder_(NULL) {}
+        decoder_(nullptr) {}
 
   virtual ~AudioDecoderTest() {}
 
@@ -113,7 +113,7 @@ class AudioDecoderTest : public ::testing::Test {
 
   virtual void TearDown() {
     delete decoder_;
-    decoder_ = NULL;
+    decoder_ = nullptr;
   }
 
   virtual void InitEncoder() { }