Replace NULL with nullptr in all C++ files.

webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc

Index: webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc
diff --git a/webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc b/webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc
index 85d0b46e79f72879db7fa0f7053888d7fe19fc2a..0a6c41b30101aeb961d37ecdba8dc15004f435c8 100644
--- a/webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc
+++ b/webrtc/tools/frame_analyzer/video_quality_analysis_unittest.cc
@@ -30,14 +30,14 @@ class VideoQualityAnalysisTest : public ::testing::Test {
     std::string log_filename = webrtc::test::OutputPath() +
         "VideoQualityAnalysisTest.log";
     logfile_ = fopen(log_filename.c_str(), "w");
-    ASSERT_TRUE(logfile_ != NULL);
+    ASSERT_TRUE(logfile_ != nullptr);
   }
   static void TearDownTestCase() {
     ASSERT_EQ(0, fclose(logfile_));
   }
   static FILE* logfile_;
 };
-FILE* VideoQualityAnalysisTest::logfile_ = NULL;
+FILE* VideoQualityAnalysisTest::logfile_ = nullptr;
 
 TEST_F(VideoQualityAnalysisTest, MatchExtractedY4mFrame) {
   std::string video_file =