[Extensions] Code cleanup - const &s

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/api/data_reduction_proxy/data_reduction_proxy_api.h"
 
 #include <utility>
 #include <vector>
 
 #include "chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.h"
@@ skipping 30 matching lines @@
 
 void DataReductionProxyGetDataUsageFunction::ReplyWithDataUsage(
     std::unique_ptr<std::vector<data_reduction_proxy::DataUsageBucket>>
         data_usage) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   std::unique_ptr<base::ListValue> data_usage_buckets(new base::ListValue());
   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());
         usage->SetDouble("data_used", site_usage.data_used());
         usage->SetDouble("original_size", site_usage.original_size());
         site_usage_list->Append(std::move(usage));
       }
       connection_usage_list->Append(std::move(site_usage_list));
     }
     data_usage_buckets->Append(std::move(connection_usage_list));
   }
 
   std::unique_ptr<base::DictionaryValue> result(new base::DictionaryValue());
   result->Set("data_usage_buckets", std::move(data_usage_buckets));
   Respond(OneArgument(std::move(result)));
 }
 
 }  // namespace extensions