Cleanup: Pass std::string as const reference from google_apis/ and components/gcm_driver/

google_apis/gaia/account_tracker.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 "google_apis/gaia/account_tracker.h"
 
 #include "base/logging.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 159 matching lines @@
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "422460 AccountTracker::NotifySignInChanged"));
 
   DCHECK(!account.ids.gaia.empty());
   FOR_EACH_OBSERVER(Observer,
                     observer_list_,
                     OnAccountSignInChanged(account.ids, account.is_signed_in));
 }
 
-void AccountTracker::UpdateSignInState(const std::string account_key,
+void AccountTracker::UpdateSignInState(const std::string& account_key,
                                        bool is_signed_in) {
   // TODO(robliao): Remove ScopedTracker below once https://crbug.com/422460 is
   // fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "422460 AccountTracker::UpdateSignInState"));
 
   StartTrackingAccount(account_key);
   AccountState& account = accounts_[account_key];
   bool needs_gaia_id = account.ids.gaia.empty();
   bool was_signed_in = account.is_signed_in;
   account.is_signed_in = is_signed_in;
 
   if (needs_gaia_id && is_signed_in)
     StartFetchingUserInfo(account_key);
 
   if (!needs_gaia_id && (was_signed_in != is_signed_in))
     NotifySignInChanged(account);
 }
 
-void AccountTracker::StartTrackingAccount(const std::string account_key) {
+void AccountTracker::StartTrackingAccount(const std::string& account_key) {
   // TODO(robliao): Remove ScopedTracker below once https://crbug.com/422460 is
   // fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "422460 AccountTracker::StartTrackingAccount"));
 
   if (!ContainsKey(accounts_, account_key)) {
     DVLOG(1) << "StartTracking " << account_key;
     AccountState account_state;
     account_state.ids.account_key = account_key;
     account_state.ids.email = account_key;
     account_state.is_signed_in = false;
     accounts_.insert(make_pair(account_key, account_state));
   }
 }
 
-void AccountTracker::StopTrackingAccount(const std::string account_key) {
+void AccountTracker::StopTrackingAccount(const std::string& account_key) {

[Roger Tawa OOO till Jul 10th, 2015/09/20 20:40:08]

I don't think this one can be changed without further cleanup.  When line 235
calls StopTrackingAccount(), the key it passes is from the |accounts_| map. 
When the entry is removed at line 226, the |account_key| argument is deleted. 
The behaviour at lines 229 and 230 becomes undefined.

One solution is to make a copy of string at line 235.  A better solution would
be to make a copy of key inside this function and then only use the copy. 
Either way please add a comment to explain what is happening.

[ki.stfu, 2015/09/21 06:15:39]

Thanks for catching it!
I think we can leave it as is, instead of passing the account_key by reference
and then copying it to a local variable.

   DVLOG(1) << "StopTracking " << account_key;
   if (ContainsKey(accounts_, account_key)) {
     AccountState& account = accounts_[account_key];
     if (!account.ids.gaia.empty()) {
       UpdateSignInState(account_key, false);
       NotifyAccountRemoved(account);
     }
     accounts_.erase(account_key);
   }
 
   if (ContainsKey(user_info_requests_, account_key))
     DeleteFetcher(user_info_requests_[account_key]);
 }
 
 void AccountTracker::StopTrackingAllAccounts() {
   while (!accounts_.empty())
     StopTrackingAccount(accounts_.begin()->first);
 }
 
-void AccountTracker::StartFetchingUserInfo(const std::string account_key) {
+void AccountTracker::StartFetchingUserInfo(const std::string& account_key) {
   // TODO(robliao): Remove ScopedTracker below once https://crbug.com/422460 is
   // fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "422460 AccountTracker::StartFetchingUserInfo"));
 
   if (ContainsKey(user_info_requests_, account_key)) {
     // TODO(robliao): Remove ScopedTracker below once https://crbug.com/422460
     // is fixed.
     tracked_objects::ScopedTracker tracking_profile1(
@@ skipping 132 matching lines @@
                                "AccountIdFetcher",
                                this,
                                "OnNetworkError",
                                "response_code",
                                response_code);
   LOG(ERROR) << "OnNetworkError " << response_code;
   tracker_->OnUserInfoFetchFailure(this);
 }
 
 }  // namespace gaia