Replace NULL with nullptr in all C++ files.

webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc

Index: webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc
diff --git a/webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc b/webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc
index ab484e9bb52b96eeac84d7d9723ccf99615649df..e48c2650ea0432acad37d38fa41a3892e0dd11a6 100644
--- a/webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc
+++ b/webrtc/tools/frame_analyzer/reference_less_video_analysis_lib.cc
@@ -40,9 +40,9 @@ void get_height_width_fps(int *height, int *width, int *fps,
   char *save_ptr;
   char *token = strtok_r(frame_header, " ", &save_ptr);
 
-  while (token != NULL) {
+  while (token != nullptr) {
     file_header_stats[no_of_stats++] = token;
-    token = strtok_r(NULL, " ", &save_ptr);
+    token = strtok_r(nullptr, " ", &save_ptr);
   }
 
   *width = std::stoi(file_header_stats[1].erase(0, 1));