Replace NULL with nullptr in all C++ files.

webrtc/media/base/streamparams.cc

Index: webrtc/media/base/streamparams.cc
diff --git a/webrtc/media/base/streamparams.cc b/webrtc/media/base/streamparams.cc
index 2bbf04563be47b6de7e0ee69b966e6c649cf00cd..86c3edf91a81912a0bc0a34c9039795e3c9f07fb 100644
--- a/webrtc/media/base/streamparams.cc
+++ b/webrtc/media/base/streamparams.cc
@@ -147,7 +147,7 @@ std::string StreamParams::ToString() const {
 }
 void StreamParams::GetPrimarySsrcs(std::vector<uint32_t>* ssrcs) const {
   const SsrcGroup* sim_group = get_ssrc_group(kSimSsrcGroupSemantics);
-  if (sim_group == NULL) {
+  if (sim_group == nullptr) {
     ssrcs->push_back(first_ssrc());
   } else {
     for (size_t i = 0; i < sim_group->ssrcs.size(); ++i) {
@@ -243,7 +243,7 @@ static void RemoveFirst(std::list<uint32_t>* ssrcs, uint32_t value) {
 
 bool IsSimulcastStream(const StreamParams& sp) {
   const SsrcGroup* const sg = sp.get_ssrc_group(kSimSsrcGroupSemantics);
-  if (sg == NULL || sg->ssrcs.size() < 2) {
+  if (sg == nullptr || sg->ssrcs.size() < 2) {
     return false;
   }
   // Start with all StreamParams SSRCs. Remove simulcast SSRCs (from sg) and