Replace NULL with nullptr in all C++ files.

webrtc/test/testsupport/fileutils.cc

Index: webrtc/test/testsupport/fileutils.cc
diff --git a/webrtc/test/testsupport/fileutils.cc b/webrtc/test/testsupport/fileutils.cc
index 2d3ea00925a10fc3ea7306eaf0454e41f4e8658f..a713452a87d8888962b01b6dbe7b96279835049c 100644
--- a/webrtc/test/testsupport/fileutils.cc
+++ b/webrtc/test/testsupport/fileutils.cc
@@ -138,7 +138,7 @@ std::string ProjectRootPath() {
 #ifdef WIN32
   BOOL succeeded = PathCanonicalizeA(canonical_path, path.c_str());
 #else
-  bool succeeded = realpath(path.c_str(), canonical_path) != NULL;
+  bool succeeded = realpath(path.c_str(), canonical_path) != nullptr;
 #endif
   if (succeeded) {
     path = std::string(canonical_path) + kPathDelimiter;
@@ -274,7 +274,7 @@ std::string ResourcePath(const std::string& name,
 size_t GetFileSize(const std::string& filename) {
   FILE* f = fopen(filename.c_str(), "rb");
   size_t size = 0;
-  if (f != NULL) {
+  if (f != nullptr) {
     if (fseek(f, 0, SEEK_END) == 0) {
       size = ftell(f);
     }