Move ASCIIToWide and ASCIIToUTF16 to utf_string_conversions.h. I've found it...

base/command_line.cc

 // Copyright (c) 2010 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 "base/command_line.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <shellapi.h>
 #elif defined(OS_POSIX)
 #include <limits.h>
 #include <stdlib.h>
 #include <unistd.h>
 #endif
 #if defined(OS_LINUX)
 #include <sys/prctl.h>
 #endif
 
 #include <algorithm>
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/singleton.h"
-#include "base/string_piece.h"
 #include "base/string_util.h"
 #include "base/sys_string_conversions.h"
+#include "base/utf_string_conversions.h"
 
 #if defined(OS_LINUX)
 // Linux/glibc doesn't natively have setproctitle().
 #include "base/setproctitle_linux.h"
 #endif
 
 CommandLine* CommandLine::current_process_commandline_ = NULL;
 
 // Since we use a lazy match, make sure that longer versions (like L"--")
 // are listed before shorter versions (like L"-") of similar prefixes.
@@ skipping 434 matching lines @@
 #endif
 
 void CommandLine::AppendSwitchWithValue(const std::string& switch_string,
                                         const std::string& value_string) {
   AppendSwitchWithValue(switch_string, ASCIIToWide(value_string));
 }
 
 // private
 CommandLine::CommandLine() {
 }