Revert of Move JoinString to the base namespace

ui/message_center/cocoa/notification_controller.mm

 // 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.
 
 #import "ui/message_center/cocoa/notification_controller.h"
 
 #include <algorithm>
 
 #include "base/mac/foundation_util.h"
 #include "base/strings/string_util.h"
@@ skipping 865 matching lines @@
     // too wide, that line will be further elided by the gfx::ElideText below.
     base::string16 last =
         wrapped[lines - 1] + base::UTF8ToUTF16(gfx::kEllipsis);
     if (gfx::GetStringWidth(last, font_list) > width)
       last = gfx::ElideText(last, font_list, width, gfx::ELIDE_TAIL);
     wrapped.resize(lines - 1);
     wrapped.push_back(last);
   }
 
   *actualLines = wrapped.size();
-  return lines == 1 ? wrapped[0]
-                    : base::JoinString(wrapped, base::ASCIIToUTF16("\n"));
+  return lines == 1 ? wrapped[0] : JoinString(wrapped, '\n');
 }
 
 - (base::string16)wrapText:(const base::string16&)text
                    forFont:(NSFont*)nsfont
           maxNumberOfLines:(size_t)lines {
   size_t unused;
   return [self wrapText:text
                 forFont:nsfont
        maxNumberOfLines:lines
             actualLines:&unused];
 }
 
 @end