Replace NULL with nullptr in all C++ files.

webrtc/tools/frame_analyzer/frame_analyzer.cc

Index: webrtc/tools/frame_analyzer/frame_analyzer.cc
diff --git a/webrtc/tools/frame_analyzer/frame_analyzer.cc b/webrtc/tools/frame_analyzer/frame_analyzer.cc
index 0a3be1939ec7eec33c09122b49a6260b8e7cdf71..5186ced5b7239dfa7b92ea79cba870cd7069564a 100644
--- a/webrtc/tools/frame_analyzer/frame_analyzer.cc
+++ b/webrtc/tools/frame_analyzer/frame_analyzer.cc
@@ -86,8 +86,8 @@ int main(int argc, char** argv) {
   }
   parser.PrintEnteredFlags();
 
-  int width = strtol((parser.GetFlag("width")).c_str(), NULL, 10);
-  int height = strtol((parser.GetFlag("height")).c_str(), NULL, 10);
+  int width = strtol((parser.GetFlag("width")).c_str(), nullptr, 10);
+  int height = strtol((parser.GetFlag("height")).c_str(), nullptr, 10);
 
   if (width <= 0 || height <= 0) {
     fprintf(stderr, "Error: width or height cannot be <= 0!\n");