Revert of Move JoinString to the base namespace

chrome/browser/thumbnails/thumbnail_list_source.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 "chrome/browser/thumbnails/thumbnail_list_source.h"
 
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 146 matching lines @@
   if (num_mv_with_thumb > 0) {
     out.push_back("<h2>TopSites URLs with Thumbnails</h2>\n");
     RenderMostVisitedURLList(mvurl_list, base64_encoded_pngs, true, &out);
   }
   if (num_mv_with_thumb < num_mv) {
     out.push_back("<h2>TopSites URLs without Thumbnails</h2>\n");
     RenderMostVisitedURLList(mvurl_list, base64_encoded_pngs, false, &out);
   }
   out.push_back(kHtmlFooter);
 
-  std::string out_html = base::JoinString(out, base::StringPiece());
+  std::string out_html = JoinString(out, "");
   callback.Run(base::RefCountedString::TakeString(&out_html));
 }