Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc b/webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc
index f22f1082621d5daf60fd1c0d5bcf40a4c95deccc..3c418bfa93ecfaecca86ce7556fdb911c79e2571 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_format_h264_unittest.cc
@@ -547,7 +547,7 @@ class RtpDepacketizerH264Test : public ::testing::Test {
   void ExpectPacket(RtpDepacketizer::ParsedPayload* parsed_payload,
                     const uint8_t* data,
                     size_t length) {
-    ASSERT_TRUE(parsed_payload != NULL);
+    ASSERT_TRUE(parsed_payload != nullptr);
     EXPECT_THAT(std::vector<uint8_t>(
                     parsed_payload->payload,
                     parsed_payload->payload + parsed_payload->payload_length),