Change uses of base::JoinString to pass StringPieces where possible.

chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos_unittest.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 <stddef.h>
 
 #include "ash/common/shelf/shelf_widget.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_controller.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_window_manager.h"
 #include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm/wm_event.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/content/shell_content_state.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/ash_test_environment_content.h"
 #include "ash/test/ash_test_helper.h"
 #include "ash/test/test_shell_delegate.h"
 #include "ash/wm/window_state_aura.h"
 #include "ash/wm/window_util.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "chrome/browser/chromeos/login/users/fake_chrome_user_manager.h"
 #include "chrome/browser/chromeos/login/users/scoped_user_manager_enabler.h"
 #include "chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h"
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/ui/ash/chrome_new_window_client.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos.h"
@@ skipping 333 matching lines @@
     s += "]";
   }
   return s;
 }
 
 std::string
 MultiUserWindowManagerChromeOSTest::GetOwnersOfVisibleWindowsAsString() {
   std::set<AccountId> owners;
   multi_user_window_manager_->GetOwnersOfVisibleWindows(&owners);
 
-  std::vector<std::string> owner_list;
+  std::vector<base::StringPiece> owner_list;
   for (auto& owner : owners)
     owner_list.push_back(owner.GetUserEmail());
   return base::JoinString(owner_list, " ");
 }
 
 // Testing basic assumptions like default state and existence of manager.
 TEST_F(MultiUserWindowManagerChromeOSTest, BasicTests) {
   SetUpForThisManyWindows(3);
   // Check the basic assumptions: All windows are visible and there is no owner.
   EXPECT_EQ("S[], S[], S[]", GetStatus());
@@ skipping 1186 matching lines @@
   user_manager()->SwitchActiveUser(account_id_B);
   multi_user_window_manager()->ActiveUserChanged(
       user_manager()->FindUser(account_id_B));
   EXPECT_EQ(browser.get(), BrowserList::GetInstance()->GetLastActive());
   EXPECT_EQ(nullptr, wm::GetActiveWindow());
   EXPECT_EQ(nullptr, ChromeNewWindowClient::GetActiveBrowser());
 }
 
 }  // namespace test
 }  // namespace ash