Cleanup: Pass std::string as const reference if possible

components/signin/core/browser/account_tracker_service_unittest.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 <algorithm>
 #include <vector>
 
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/prefs/testing_pref_service.h"
@@ skipping 30 matching lines @@
       \"id\": \"%s\",         \
       \"email\": \"%s\",      \
       \"hd\": \"\",           \
     }";
 
 enum TrackingEventType {
   UPDATED,
   REMOVED,
 };
 
-std::string AccountIdToEmail(const std::string account_id) {
+std::string AccountIdToEmail(const std::string& account_id) {
   return account_id + "@gmail.com";
 }
 
-std::string AccountIdToGaiaId(const std::string account_id) {
+std::string AccountIdToGaiaId(const std::string& account_id) {
   return "gaia-" + account_id;
 }
 
-std::string AccountIdToFullName(const std::string account_id) {
+std::string AccountIdToFullName(const std::string& account_id) {
   return "full-name-" + account_id;
 }
 
-std::string AccountIdToGivenName(const std::string account_id) {
+std::string AccountIdToGivenName(const std::string& account_id) {
   return "given-name-" + account_id;
 }
 
-std::string AccountIdToLocale(const std::string account_id) {
+std::string AccountIdToLocale(const std::string& account_id) {
   return "locale-" + account_id;
 }
 
-std::string AccountIdToPictureURL(const std::string account_id) {
+std::string AccountIdToPictureURL(const std::string& account_id) {
   return "picture_url-" + account_id;
 }
 
-void CheckAccountDetails(const std::string account_id,
+void CheckAccountDetails(const std::string& account_id,
                          const AccountInfo& info) {
   EXPECT_EQ(account_id, info.account_id);
   EXPECT_EQ(AccountIdToGaiaId(account_id), info.gaia);
   EXPECT_EQ(AccountIdToEmail(account_id), info.email);
   EXPECT_EQ(AccountTrackerService::kNoHostedDomainFound,
             info.hosted_domain);
   EXPECT_EQ(AccountIdToFullName(account_id), info.full_name);
   EXPECT_EQ(AccountIdToGivenName(account_id), info.given_name);
   EXPECT_EQ(AccountIdToLocale(account_id), info.locale);
 }
@@ skipping 1078 matching lines @@
   ASSERT_FALSE(info.is_child_account);
   ASSERT_TRUE(observer.CheckEvents(TrackingEvent(UPDATED, child_id)));
 
   SimulateTokenRevoked(child_id);
   ASSERT_TRUE(observer.CheckEvents(TrackingEvent(REMOVED, child_id)));
 
   tracker.RemoveObserver(&observer);
   fetcher.Shutdown();
   tracker.Shutdown();
 }