Convert JsonWriter::Write to taking a const ref for the in-param

chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc

Index: chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc
diff --git a/chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc b/chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc
index ef6108e4b86196626942a7967243322d3ad75fb0..a0c5de40413dc5095bdd10b2d3969f505e3573cb 100644
--- a/chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc
+++ b/chrome/browser/ui/webui/options/sync_setup_handler_unittest.cc
@@ -93,7 +93,7 @@ std::string GetConfiguration(const base::DictionaryValue* extra_values,
   result.SetBoolean("wifiCredentialsSynced",
                     types.Has(syncer::WIFI_CREDENTIALS));
   std::string args;
-  base::JSONWriter::Write(&result, &args);
+  base::JSONWriter::Write(result, &args);
   return args;
 }