Move EmptyString, kWhitespace and the BOM to base.

chrome/browser/ui/ash/multi_user/multi_user_window_manager_stub.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/ash/multi_user/multi_user_window_manager_stub.h"
 
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 
 namespace chrome {
 
 void MultiUserWindowManagerStub::SetWindowOwner(aura::Window* window,
                                                const std::string& user_id) {
   NOTIMPLEMENTED();
 }
 
 const std::string& MultiUserWindowManagerStub::GetWindowOwner(
     aura::Window* window) {
-  return EmptyString();
+  return base::EmptyString();
 }
 
 void MultiUserWindowManagerStub::ShowWindowForUser(aura::Window* window,
                                                   const std::string& user_id) {
   NOTIMPLEMENTED();
 }
 
 bool MultiUserWindowManagerStub::AreWindowsSharedAmongUsers() {
   return false;
 }
 
 bool MultiUserWindowManagerStub::IsWindowOnDesktopOfUser(
     aura::Window* window,
     const std::string& user_id) {
   return true;
 }
 
 const std::string& MultiUserWindowManagerStub::GetUserPresentingWindow(
     aura::Window* window) {
-  return EmptyString();
+  return base::EmptyString();
 }
 
 void MultiUserWindowManagerStub::AddUser(Profile* profile) {
   NOTIMPLEMENTED();
 }
 
 }  // namespace chrome