This CL replaces user_manager::UserID with AccountId.

chrome/browser/extensions/api/file_system/file_system_apitest_chromeos.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/extensions/api/file_system/file_system_api.h"
 
 #include "base/callback.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/location.h"
@@ skipping 247 matching lines @@
         mount_point_path, file_manager::VOLUME_TYPE_TESTING,
         chromeos::DEVICE_TYPE_UNKNOWN, read_only);
   }
 
   // Simulates entering the kiosk session.
   void EnterKioskSession() {
     fake_user_manager_ = new chromeos::FakeChromeUserManager();
     user_manager_enabler_.reset(
         new chromeos::ScopedUserManagerEnabler(fake_user_manager_));
 
-    const std::string kKioskLogin = "kiosk@foobar.com";
-    fake_user_manager_->AddKioskAppUser(kKioskLogin);
-    fake_user_manager_->LoginUser(kKioskLogin);
+    const AccountId kiosk_app_account_id =
+        AccountId::FromUserEmail("kiosk@foobar.com");
+    fake_user_manager_->AddKioskAppUser(kiosk_app_account_id);
+    fake_user_manager_->LoginUser(kiosk_app_account_id);
   }
 };
 
 IN_PROC_BROWSER_TEST_F(FileSystemApiTestForDrive,
                        FileSystemApiOpenExistingFileTest) {
   base::FilePath test_file = drive::util::GetDriveMountPointPath(
       browser()->profile()).AppendASCII("root/open_existing.txt");
   FileSystemChooseEntryFunction::SkipPickerAndAlwaysSelectPathForTest(
       &test_file);
   ASSERT_TRUE(RunPlatformAppTest("api_test/file_system/open_existing"))
@@ skipping 210 matching lines @@
       profile(), extensions::api::file_system::OnVolumeListChanged::kEventName,
       kTestingExtensionId,
       base::Bind(&FileSystemApiTestForRequestFileSystem::MountFakeVolume,
                  this));
 
   ASSERT_TRUE(RunPlatformAppTest("api_test/file_system/on_volume_list_changed"))
       << message_;
 }
 
 }  // namespace extensions