Revert of Move JoinString to the base namespace

chrome/browser/extensions/extension_install_prompt.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 "chrome/browser/extensions/extension_install_prompt.h"
 
 #include <map>
 
 #include "base/command_line.h"
 #include "base/location.h"
@@ skipping 251 matching lines @@
     install_permissions.permissions.push_back(str.message);
     // Add a dash to the front of each permission detail.
     base::string16 details;
     if (!str.submessages.empty()) {
       std::vector<base::string16> detail_lines_with_bullets;
       for (const auto& detail_line : str.submessages) {
         detail_lines_with_bullets.push_back(base::ASCIIToUTF16("- ") +
                                             detail_line);
       }
 
-      details = base::JoinString(detail_lines_with_bullets,
-                                 base::ASCIIToUTF16("\n"));
+      details = JoinString(detail_lines_with_bullets, '\n');
     }
     install_permissions.details.push_back(details);
     install_permissions.is_showing_details.push_back(false);
   }
 }
 
 void ExtensionInstallPrompt::Prompt::SetIsShowingDetails(
     DetailsType type,
     size_t index,
     bool is_showing_details) {
@@ skipping 651 matching lines @@
   if (show_params_->WasParentDestroyed()) {
     delegate_->InstallUIAbort(false);
     return;
   }
 
   if (show_dialog_callback_.is_null())
     GetDefaultShowDialogCallback().Run(show_params_.get(), delegate_, prompt_);
   else
     show_dialog_callback_.Run(show_params_.get(), delegate_, prompt_);
 }