Replace NULL with nullptr or null in webrtc/base/.

webrtc/base/stringencode.cc

Index: webrtc/base/stringencode.cc
diff --git a/webrtc/base/stringencode.cc b/webrtc/base/stringencode.cc
index 7c11a05e3e916c5a9c1015a0208448182bb01286..c7d206fd9329724071095ec675681e98df65d271 100644
--- a/webrtc/base/stringencode.cc
+++ b/webrtc/base/stringencode.cc
@@ -141,7 +141,7 @@ const unsigned char ASCII_CLASS[128] = {
 
 size_t url_encode(char * buffer, size_t buflen,
                   const char * source, size_t srclen) {
-  if (NULL == buffer)
+  if (nullptr == buffer)
     return srclen * 3 + 1;
   if (buflen <= 0)
     return 0;
@@ -167,7 +167,7 @@ size_t url_encode(char * buffer, size_t buflen,
 
 size_t url_decode(char * buffer, size_t buflen,
                   const char * source, size_t srclen) {
-  if (NULL == buffer)
+  if (nullptr == buffer)
     return srclen + 1;
   if (buflen <= 0)
     return 0;
@@ -546,7 +546,7 @@ size_t transform(std::string& value, size_t maxlen, const std::string& source,
 
 std::string s_transform(const std::string& source, Transform t) {
   // Ask transformation function to approximate the destination size (returns upper bound)
-  size_t maxlen = t(NULL, 0, source.data(), source.length());
+  size_t maxlen = t(nullptr, 0, source.data(), source.length());
   char * buffer = STACK_ARRAY(char, maxlen);
   size_t len = t(buffer, maxlen, source.data(), source.length());
   std::string result(buffer, len);