[Extensions] Code cleanup - const &s

chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc

Index: chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc
diff --git a/chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc b/chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc
index a2563e222b3270dba131789a0ca288e45ec5990c..1f84f6a6f96a00ec6d12e52fd92168d09d44ca8a 100644
--- a/chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc
+++ b/chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.cc
@@ -48,9 +48,9 @@ void DataReductionProxyGetDataUsageFunction::ReplyWithDataUsage(
   for (const auto& data_usage_bucket : *data_usage) {
     std::unique_ptr<base::ListValue> connection_usage_list(
         new base::ListValue());
-    for (auto connection_usage : data_usage_bucket.connection_usage()) {
+    for (const auto& connection_usage : data_usage_bucket.connection_usage()) {
       std::unique_ptr<base::ListValue> site_usage_list(new base::ListValue());
-      for (auto site_usage : connection_usage.site_usage()) {
+      for (const auto& site_usage : connection_usage.site_usage()) {
         std::unique_ptr<base::DictionaryValue> usage(
             new base::DictionaryValue());
         usage->SetString("hostname", site_usage.hostname());