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

components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc

Index: components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc
diff --git a/components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc b/components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc
index aeac80ffce9e664f8dc51119c2d618ebf04b7c86..3abb3e1baaa3a876d7e6c517a607bef03be680ba 100644
--- a/components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc
+++ b/components/sync/engine_impl/sync_encryption_handler_impl_unittest.cc
@@ -655,9 +655,9 @@ TEST_F(SyncEncryptionHandlerImplTest, SetKeystoreMigratesAndUpdatesBootstrap) {
       decoded_bootstrap, &decrypted_bootstrap));
   JSONStringValueDeserializer json(decrypted_bootstrap);
   std::unique_ptr<base::Value> deserialized_keystore_keys(
-      json.Deserialize(NULL, NULL));
+      json.Deserialize(nullptr, nullptr));
   ASSERT_TRUE(deserialized_keystore_keys.get());
-  base::ListValue* keystore_list = NULL;
+  base::ListValue* keystore_list = nullptr;
   deserialized_keystore_keys->GetAsList(&keystore_list);
   ASSERT_TRUE(keystore_list);
   ASSERT_EQ(2U, keystore_list->GetSize());