Mojo: NULL -> nullptr in mojo/system and mojo/embedder.

mojo/embedder/test_embedder.cc

Index: mojo/embedder/test_embedder.cc
diff --git a/mojo/embedder/test_embedder.cc b/mojo/embedder/test_embedder.cc
index 7f50abb9de9d9b81d0be538f59081467930f0bac..f3884233c11c21109d039cdaa0db94a2449799dd 100644
--- a/mojo/embedder/test_embedder.cc
+++ b/mojo/embedder/test_embedder.cc
@@ -48,7 +48,7 @@ void InitWithSimplePlatformSupport() {
 bool Shutdown() {
   system::Core* core = system::entrypoints::GetCore();
   CHECK(core);
-  system::entrypoints::SetCore(NULL);
+  system::entrypoints::SetCore(nullptr);
 
   bool rv = system::internal::ShutdownCheckNoLeaks(core);
   delete core;