Move JoinString to the base namespace

ash/system/chromeos/tray_display.cc

 // Copyright (c) 2012 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 "ash/system/chromeos/tray_display.h"
 
 #include <vector>
 
 #include "ash/content/display/screen_orientation_controller_chromeos.h"
 #include "ash/display/display_controller.h"
@@ skipping 89 matching lines @@
     lines.push_back(GetDisplayInfoLine(internal_id));
   }
 
   for (size_t i = 0; i < display_manager->GetNumDisplays(); ++i) {
     int64 id = display_manager->GetDisplayAt(i).id();
     if (id == internal_id)
       continue;
     lines.push_back(GetDisplayInfoLine(id));
   }
 
-  return JoinString(lines, '\n');
+  return base::JoinString(lines, base::ASCIIToUTF16("\n"));
 }
 
 void OpenSettings() {
   // switch is intentionally introduced without default, to cause an error when
   // a new type of login status is introduced.
   switch (Shell::GetInstance()->system_tray_delegate()->GetUserLoginStatus()) {
     case user::LOGGED_IN_NONE:
     case user::LOGGED_IN_LOCKED:
       return;
 
@@ skipping 325 matching lines @@
 bool TrayDisplay::GetAccessibleStateForTesting(ui::AXViewState* state) {
   views::View* view = default_;
   if (view) {
     view->GetAccessibleState(state);
     return true;
   }
   return false;
 }
 
 }  // namespace ash