We should use UserID object to identify users instead of username.

chrome/browser/ui/app_list/app_list_service_impl.cc

 // Copyright 2013 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/ui/app_list/app_list_service_impl.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 82 matching lines @@
 
   void LoadProfileAsync(const base::FilePath& path,
                         base::Callback<void(Profile*)> callback) override {
     profile_manager_->CreateProfileAsync(
         path,
         base::Bind(&ProfileStoreImpl::OnProfileCreated,
                    weak_factory_.GetWeakPtr(),
                    callback),
         base::string16(),
         base::string16(),
-        std::string());
+        user_manager::UserID(std::string(), std::string()));
   }
 
   void OnProfileCreated(base::Callback<void(Profile*)> callback,
                         Profile* profile,
                         Profile::CreateStatus status) {
     switch (status) {
       case Profile::CREATE_STATUS_CREATED:
         break;
       case Profile::CREATE_STATUS_INITIALIZED:
         callback.Run(profile);
@@ skipping 332 matching lines @@
   if (!base::MessageLoop::current())
     return;  // In a unit test.
 
   // Send app list usage stats after a delay.
   const int kSendUsageStatsDelay = 5;
   base::MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&AppListServiceImpl::SendAppListStats),
       base::TimeDelta::FromSeconds(kSendUsageStatsDelay));
 }