Use SCOPED_UMA_HISTOGRAM_TIMER in SupervisedUserSiteList.

chrome/browser/supervised_user/supervised_user_site_list.cc

 // Copyright 2014 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/supervised_user/supervised_user_site_list.h"
 
 #include "base/files/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/logging.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/task_runner_util.h"
 #include "base/values.h"
 #include "chrome/browser/safe_json_parser.h"
 #include "content/public/browser/browser_thread.h"
 #include "url/gurl.h"
 
 const int kSitelistFormatVersion = 1;
 
 const char kHostnameHashesKey[] = "hostname_hashes";
 const char kNameKey[] = "name";
 const char kSitesKey[] = "sites";
 const char kSitelistFormatVersionKey[] = "version";
 const char kUrlKey[] = "url";
 const char kWhitelistKey[] = "whitelist";
 
 namespace {
 
 bool g_load_in_process = false;
 
 std::string ReadFileOnBlockingThread(const base::FilePath& path) {
-  base::TimeTicks start = base::TimeTicks::Now();
+  SCOPED_UMA_HISTOGRAM_TIMER("ManagedUsers.Whitelist.ReadDuration");
   std::string contents;
   base::ReadFileToString(path, &contents);
-  UMA_HISTOGRAM_TIMES("ManagedUsers.Whitelist.ReadDuration",
-                      base::TimeTicks::Now() - start);
   return contents;
 }
 
 void HandleError(const base::FilePath& path, const std::string& error) {
   LOG(ERROR) << "Couldn't load site list " << path.value() << ": " << error;
 }
 
 // Takes a DictionaryValue entry from the JSON file and fills the whitelist
 // (via URL patterns or hostname hashes) and the URL in the corresponding Site
 // struct.
@@ skipping 147 matching lines @@
 
   base::ListValue* sites = nullptr;
   if (!dict->GetList(kSitesKey, &sites)) {
     LOG(ERROR) << "Site list " << path.value()
                << " does not contain any sites";
     return;
   }
 
   callback.Run(make_scoped_refptr(new SupervisedUserSiteList(*sites)));
 }