Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/file_player_unittests.cc

Index: webrtc/voice_engine/file_player_unittests.cc
diff --git a/webrtc/voice_engine/file_player_unittests.cc b/webrtc/voice_engine/file_player_unittests.cc
index d41f4044b4ae5a7104aff7f562272ee5dbf4f533..93d3f283a6108efe2ba7d91270cbba00ce9d5038 100644
--- a/webrtc/voice_engine/file_player_unittests.cc
+++ b/webrtc/voice_engine/file_player_unittests.cc
@@ -35,14 +35,14 @@ class FilePlayerTest : public ::testing::Test {
 
   FilePlayerTest()
       : player_(FilePlayer::CreateFilePlayer(kId, kFileFormat)),
-        output_file_(NULL) {}
+        output_file_(nullptr) {}
 
   void SetUp() override {
     if (FLAGS_file_player_output) {
       std::string output_file =
           webrtc::test::OutputPath() + "file_player_unittest_out.pcm";
       output_file_ = fopen(output_file.c_str(), "wb");
-      ASSERT_TRUE(output_file_ != NULL);
+      ASSERT_TRUE(output_file_ != nullptr);
     }
   }
 
@@ -56,7 +56,7 @@ class FilePlayerTest : public ::testing::Test {
                         int output_length_ms) {
     const float kScaling = 1;
     ASSERT_EQ(0, player_->StartPlayingFile(input_file.c_str(), false, 0,
-                                           kScaling, 0, 0, NULL));
+                                           kScaling, 0, 0, nullptr));
     rtc::Md5Digest checksum;
     for (int i = 0; i < output_length_ms / 10; ++i) {
       int16_t out[10 * kSampleRateHz / 1000] = {0};