Move JoinString to the base namespace

tools/set_default_handler/set_default_handler_main.cc

 // Copyright (c) 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.
 
 // Makes a given program ("Google Chrome" by default) the default handler for
 // some URL protocol ("http" by default) on Windows 8. These defaults can be
 // overridden via the --program and --protocol command line switches.
 
 #include <windows.h>
 
@@ skipping 38 matching lines @@
 
   std::vector<base::string16> choices;
   HRESULT result = S_OK;
   win8::OpenWithDialogController controller;
   result = controller.RunSynchronously(NULL, protocol, program, &choices);
 
   if (SUCCEEDED(result)) {
     printf("success\n");
   } else if (!choices.empty()) {
     printf("failed to set program. possible choices: %ls\n",
-           JoinString(choices, L", ").c_str());
+           base::JoinString(choices, L", ").c_str());
   } else {
     printf("failed with HRESULT: %0x08X\n", result);
   }
 
   return FAILED(result);
 }