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

base/string_util.h

Index: base/string_util.h
===================================================================
--- base/string_util.h	(revision 54020)
+++ base/string_util.h	(working copy)
@@ -227,12 +227,21 @@
 bool ContainsOnlyChars(const string16& input, const string16& characters);
 bool ContainsOnlyChars(const std::string& input, const std::string& characters);
 
-// These convert between ASCII (7-bit) and Wide/UTF16 strings.
+// Converts to 7-bit ASCII by truncating. The result must be known to be ASCII
+// beforehand.
 std::string WideToASCII(const std::wstring& wide);
-std::wstring ASCIIToWide(const base::StringPiece& ascii);
 std::string UTF16ToASCII(const string16& utf16);
-string16 ASCIIToUTF16(const base::StringPiece& ascii);
 
+// Forward-declares for functions in utf_string_conversions.h. They used to
+// be here and they were moved. We keep these here so the entire project
+// doesn't need to be switched at once.
+// TODO(brettw) delete these when everybody includes utf_string_conversions.h
+// instead.
+std::wstring ASCIIToWide(const char* ascii);
+std::wstring ASCIIToWide(const std::string& ascii);
+string16 ASCIIToUTF16(const char* ascii);
+string16 ASCIIToUTF16(const std::string& ascii);
+
 // Converts the given wide string to the corresponding Latin1. This will fail
 // (return false) if any characters are more than 255.
 bool WideToLatin1(const std::wstring& wide, std::string* latin1);