Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc

Index: webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc
diff --git a/webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc b/webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc
index 3b7a53c4ab2a250f83e4a70fed06bccc572572b0..8ec4ee56734dcefb9c3e843feb80b3ed79feef84 100644
--- a/webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc
+++ b/webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc
@@ -42,7 +42,7 @@ int main(int argc, char* argv[]) {
   // Read file header and write directly to output file.
   const unsigned int kRtpDumpHeaderSize = 4 + 4 + 4 + 2 + 2;
   char firstline[FIRSTLINELEN];
-  EXPECT_TRUE(fgets(firstline, FIRSTLINELEN, inFile) != NULL);
+  EXPECT_TRUE(fgets(firstline, FIRSTLINELEN, inFile) != nullptr);
   EXPECT_GT(fputs(firstline, outFile), 0);
   EXPECT_EQ(kRtpDumpHeaderSize,
             fread(firstline, 1, kRtpDumpHeaderSize, inFile));