Add utf_string_conversions to base namespace.

chrome/browser/extensions/api/file_system/file_system_api.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/api/file_system/file_system_api.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 213 matching lines @@
     }
   }
 
   if (accept_option.extensions.get()) {
     std::vector<std::string>* list = accept_option.extensions.get();
     for (std::vector<std::string>::const_iterator iter = list->begin();
          iter != list->end(); ++iter) {
       std::string extension = *iter;
       StringToLowerASCII(&extension);
 #if defined(OS_WIN)
-      extension_set.insert(UTF8ToWide(*iter));
+      extension_set.insert(base::UTF8ToWide(*iter));
 #else
       extension_set.insert(*iter);
 #endif
     }
   }
 
   extensions->assign(extension_set.begin(), extension_set.end());
   if (extensions->empty())
     return false;
 
@@ skipping 350 matching lines @@
 
   if (entry_type == WRITABLE && !HasFileSystemWritePermission()) {
     error_ = kRequiresFileSystemWriteError;
     return false;
   }
 
   return ShowPicker(suggested_name, file_type_info, picker_type, entry_type);
 }
 
 }  // namespace extensions