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

chrome/browser/chromeos/proxy_config_service_impl_unittest.cc

Index: chrome/browser/chromeos/proxy_config_service_impl_unittest.cc
diff --git a/chrome/browser/chromeos/proxy_config_service_impl_unittest.cc b/chrome/browser/chromeos/proxy_config_service_impl_unittest.cc
index 785c48aabb1874c4491a9e8b1a34561b6e7708f1..121ef02ebde23ccb1777b0666b37a2437fa2bae6 100644
--- a/chrome/browser/chromeos/proxy_config_service_impl_unittest.cc
+++ b/chrome/browser/chromeos/proxy_config_service_impl_unittest.cc
@@ -333,7 +333,7 @@ class ProxyConfigServiceImplTest : public testing::Test {
   void SetUserConfigInShill(base::DictionaryValue* pref_proxy_config_dict) {
     std::string proxy_config;
     if (pref_proxy_config_dict)
-      base::JSONWriter::Write(pref_proxy_config_dict, &proxy_config);
+      base::JSONWriter::Write(*pref_proxy_config_dict, &proxy_config);
 
     NetworkStateHandler* network_state_handler =
         NetworkHandler::Get()->network_state_handler();