Revert of Move JoinString to the base namespace

ui/gl/gl_context.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 <string>
 
 #include "base/bind.h"
 #include "base/cancelable_callback.h"
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 82 matching lines @@
 
   std::vector<std::string> exts;
   GLint num_extensions = 0;
   glGetIntegerv(GL_NUM_EXTENSIONS, &num_extensions);
   for (GLint i = 0; i < num_extensions; ++i) {
     const char* extension = reinterpret_cast<const char*>(
         glGetStringi(GL_EXTENSIONS, i));
     DCHECK(extension != nullptr);
     exts.push_back(extension);
   }
-  return base::JoinString(exts, " ");
+  return JoinString(exts, " ");
 }
 
 std::string GLContext::GetGLVersion() {
   DCHECK(IsCurrent(nullptr));
   const char *version =
       reinterpret_cast<const char*>(glGetString(GL_VERSION));
   return std::string(version ? version : "");
 }
 
 std::string GLContext::GetGLRenderer() {
@@ skipping 151 matching lines @@
 }
 
 GLContextReal::~GLContextReal() {}
 
 void GLContextReal::SetCurrent(GLSurface* surface) {
   GLContext::SetCurrent(surface);
   current_real_context_.Pointer()->Set(surface ? this : nullptr);
 }
 
 }  // namespace gfx