Replace NULL with nullptr in all C++ files.

webrtc/test/rtp_file_reader_unittest.cc

Index: webrtc/test/rtp_file_reader_unittest.cc
diff --git a/webrtc/test/rtp_file_reader_unittest.cc b/webrtc/test/rtp_file_reader_unittest.cc
index a9cd09879e77ca6a5d06a5406747b2df7c1375d5..39aaebd0f8dc024f02f7a293f65ed2b5f1560582 100644
--- a/webrtc/test/rtp_file_reader_unittest.cc
+++ b/webrtc/test/rtp_file_reader_unittest.cc
@@ -25,7 +25,7 @@ class TestRtpFileReader : public ::testing::Test {
         test::ResourcePath("video_coding/" + filename, "rtp");
     rtp_packet_source_.reset(
         test::RtpFileReader::Create(test::RtpFileReader::kRtpDump, filepath));
-    ASSERT_TRUE(rtp_packet_source_.get() != NULL);
+    ASSERT_TRUE(rtp_packet_source_.get() != nullptr);
     headers_only_file_ = headers_only_file;
   }
 
@@ -66,7 +66,7 @@ class TestPcapFileReader : public ::testing::Test {
         test::ResourcePath("video_coding/" + filename, "pcap");
     rtp_packet_source_.reset(
         test::RtpFileReader::Create(test::RtpFileReader::kPcap, filepath));
-    ASSERT_TRUE(rtp_packet_source_.get() != NULL);
+    ASSERT_TRUE(rtp_packet_source_.get() != nullptr);
   }
 
   int CountRtpPackets() {