Replace NULL with nullptr in all C++ files.

webrtc/test/testsupport/fileutils_unittest.cc

Index: webrtc/test/testsupport/fileutils_unittest.cc
diff --git a/webrtc/test/testsupport/fileutils_unittest.cc b/webrtc/test/testsupport/fileutils_unittest.cc
index f7ddb1539bf40b643a1c5d070de598c3792ee669..98013fd742c52c5c9d28e9284ed15b62f9719480 100644
--- a/webrtc/test/testsupport/fileutils_unittest.cc
+++ b/webrtc/test/testsupport/fileutils_unittest.cc
@@ -138,7 +138,7 @@ TEST_F(FileUtilsTest, GetFileSizeExistingFile) {
   std::string temp_filename = webrtc::test::TempFilename(
       webrtc::test::OutputPath(), "fileutils_unittest");
   FILE* file = fopen(temp_filename.c_str(), "wb");
-  ASSERT_TRUE(file != NULL) << "Failed to open file: " << temp_filename;
+  ASSERT_TRUE(file != nullptr) << "Failed to open file: " << temp_filename;
   ASSERT_GT(fprintf(file, "%s",  "Dummy data"), 0) <<
       "Failed to write to file: " << temp_filename;
   fclose(file);