[cleanup] Replace uses of NULL with nullptr

Generated using clang-tidy,

tools/clang/scripts/build_clang_tools_extra.py \
  --fetch out/Default clang-tidy clang-apply-replacements
ninja -C out/Default
gn gen out/Default --export-compile-commands
cd out/Default
tools/clang/third_party/llvm/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py -p . \
  -clang-tidy-binary out/Default/tools/clang/third_party/llvm/build/bin/clang-tidy \
  -clang-apply-replacements-binary \
      out/Default/tools/clang/third_party/llvm/build/bin/clang-apply-replacements \
  -checks='-*,modernize-use-nullptr' \
  -fix

This CL was uploaded by git cl split.

Bug: webrtc:42232595
Change-Id: I356bf20cda6046c5b6d761e8d745d58f08307b99
No-Iwyu: LSC
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/391863
Auto-Submit: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#44637}
diff --git a/rtc_tools/frame_analyzer/video_quality_analysis_unittest.cc b/rtc_tools/frame_analyzer/video_quality_analysis_unittest.cc
index 2b18388..7ad8ec1 100644
--- a/rtc_tools/frame_analyzer/video_quality_analysis_unittest.cc
+++ b/rtc_tools/frame_analyzer/video_quality_analysis_unittest.cc
@@ -138,7 +138,7 @@
 
   std::string log_filename = TempFilename(test::OutputPath(), "log.log");
   FILE* logfile = fopen(log_filename.c_str(), "w");
-  ASSERT_TRUE(logfile != NULL);
+  ASSERT_TRUE(logfile != nullptr);
 
   result.max_repeated_frames = 1;
   result.max_skipped_frames = 0;