Revert of Move JoinString to the base namespace

extensions/common/permissions/usb_device_permission.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 "extensions/common/permissions/usb_device_permission.h"
 
 #include <set>
 #include <string>
 
 #include "base/logging.h"
@@ skipping 99 matching lines @@
           base::UTF8ToUTF16(vendor)));
     }
 
     // Display the catch all "device from an unknown vendor" last.
     if (found_unknown_vendor) {
       details.push_back(l10n_util::GetStringUTF16(
           IDS_EXTENSION_PROMPT_WARNING_USB_DEVICE_LIST_ITEM_UNKNOWN_VENDOR));
     }
 
     if (messages) {
-      messages->push_back(PermissionMessage(
-          PermissionMessage::kUsbDevice,
-          l10n_util::GetStringUTF16(
-              IDS_EXTENSION_PROMPT_WARNING_USB_DEVICE_LIST),
-          base::JoinString(details, base::ASCIIToUTF16("\n"))));
+      messages->push_back(
+          PermissionMessage(PermissionMessage::kUsbDevice,
+                            l10n_util::GetStringUTF16(
+                                IDS_EXTENSION_PROMPT_WARNING_USB_DEVICE_LIST),
+                            JoinString(details, base::char16('\n'))));
     }
     if (ids) {
       for (const auto& detail : details)
         ids->insert(APIPermission::kUsbDeviceList, detail);
     }
   }
 }
 
 }  // namespace
 
@@ skipping 12 matching lines @@
 }
 
 PermissionMessages UsbDevicePermission::GetMessages() const {
   DCHECK(HasMessages());
   PermissionMessages messages;
   AddPermissionsToLists(data_set_, NULL, &messages);
   return messages;
 }
 
 }  // namespace extensions