[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/syncable/entry_kernel.cc

Index: components/sync/syncable/entry_kernel.cc
diff --git a/components/sync/syncable/entry_kernel.cc b/components/sync/syncable/entry_kernel.cc
index 1e74ef7e8dd4c993d890b0ec39e925c91afdac6a..2aaf8d1dcd9126f672aab637395ce27e64d3aea5 100644
--- a/components/sync/syncable/entry_kernel.cc
+++ b/components/sync/syncable/entry_kernel.cc
@@ -224,8 +224,8 @@ std::unique_ptr<base::ListValue> EntryKernelMutationMapToValue(
 std::unique_ptr<base::DictionaryValue> EntryKernelMutationToValue(
     const EntryKernelMutation& mutation) {
   std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
-  dict->Set("original", mutation.original.ToValue(NULL));
-  dict->Set("mutated", mutation.mutated.ToValue(NULL));
+  dict->Set("original", mutation.original.ToValue(nullptr));
+  dict->Set("mutated", mutation.mutated.ToValue(nullptr));
   return dict;
 }