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

components/sync/engine_impl/sync_encryption_handler_impl.cc

Index: components/sync/engine_impl/sync_encryption_handler_impl.cc
diff --git a/components/sync/engine_impl/sync_encryption_handler_impl.cc b/components/sync/engine_impl/sync_encryption_handler_impl.cc
index f552d57d5d5b48a27fb3c3faa0ea1a48ad1c22d6..c047c75a4b75f9135e7febd6f3adbd079a155d71 100644
--- a/components/sync/engine_impl/sync_encryption_handler_impl.cc
+++ b/components/sync/engine_impl/sync_encryption_handler_impl.cc
@@ -172,10 +172,10 @@ bool UnpackKeystoreBootstrapToken(const std::string& keystore_bootstrap_token,
 
   JSONStringValueDeserializer json(decrypted_keystore_bootstrap);
   std::unique_ptr<base::Value> deserialized_keystore_keys(
-      json.Deserialize(NULL, NULL));
+      json.Deserialize(nullptr, nullptr));
   if (!deserialized_keystore_keys)
     return false;
-  base::ListValue* internal_list_value = NULL;
+  base::ListValue* internal_list_value = nullptr;
   if (!deserialized_keystore_keys->GetAsList(&internal_list_value))
     return false;
   int number_of_keystore_keys = internal_list_value->GetSize();