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

base/string_util.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/string_util.h"
 
 #include "build/build_config.h"
 
 #include <ctype.h>
 #include <errno.h>
 #include <math.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
 #include <wchar.h>
 #include <wctype.h>
 
 #include <algorithm>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/singleton.h"
 #include "base/third_party/dmg_fp/dmg_fp.h"
 #include "base/utf_string_conversion_utils.h"
+#include "base/utf_string_conversions.h"
 #include "base/third_party/icu/icu_utf.h"
 
 namespace {
 
 // Force the singleton used by Empty[W]String[16] to be a unique type. This
 // prevents other code that might accidentally use Singleton<string> from
 // getting our internal one.
 struct EmptyStrings {
   EmptyStrings() {}
   const std::string s;
@@ skipping 608 matching lines @@
 bool ContainsOnlyChars(const std::string& input,
                        const std::string& characters) {
   return ContainsOnlyCharsT(input, characters);
 }
 
 std::string WideToASCII(const std::wstring& wide) {
   DCHECK(IsStringASCII(wide)) << wide;
   return std::string(wide.begin(), wide.end());
 }
 
-std::wstring ASCIIToWide(const base::StringPiece& ascii) {
-  DCHECK(IsStringASCII(ascii)) << ascii;
-  return std::wstring(ascii.begin(), ascii.end());
-}
-
 std::string UTF16ToASCII(const string16& utf16) {
   DCHECK(IsStringASCII(utf16)) << utf16;
   return std::string(utf16.begin(), utf16.end());
 }
 
-string16 ASCIIToUTF16(const base::StringPiece& ascii) {
-  DCHECK(IsStringASCII(ascii)) << ascii;
-  return string16(ascii.begin(), ascii.end());
-}
-
 // Latin1 is just the low range of Unicode, so we can copy directly to convert.
 bool WideToLatin1(const std::wstring& wide, std::string* latin1) {
   std::string output;
   output.resize(wide.size());
   latin1->clear();
   for (size_t i = 0; i < wide.size(); i++) {
     if (wide[i] > 255)
       return false;
     output[i] = static_cast<char>(wide[i]);
   }
@@ skipping 1229 matching lines @@
   // Each input byte creates two output hex characters.
   std::string ret(size * 2, '\0');
 
   for (size_t i = 0; i < size; ++i) {
     char b = reinterpret_cast<const char*>(bytes)[i];
     ret[(i * 2)] = kHexChars[(b >> 4) & 0xf];
     ret[(i * 2) + 1] = kHexChars[b & 0xf];
   }
   return ret;
 }