Now that we deal with string16s, provide some useful conversions for them.

base/sys_string_conversions_mac.mm

 // Copyright (c) 2006-2008 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/sys_string_conversions.h"
 
 #import <Foundation/Foundation.h>
 
 #include <vector>
 
@@ skipping 97 matching lines @@
                                  in_length *
                                    sizeof(typename StringType::value_type),
                                  in_encoding,
                                  false);
 }
 
 // Specify the byte ordering explicitly, otherwise CFString will be confused
 // when strings don't carry BOMs, as they typically won't.
 static const CFStringEncoding kNarrowStringEncoding = kCFStringEncodingUTF8;
 #ifdef __BIG_ENDIAN__
-#if defined(WCHAR_T_IS_UTF16)
-static const CFStringEncoding kWideStringEncoding = kCFStringEncodingUTF16BE;
-#elif defined(WCHAR_T_IS_UTF32)
+static const CFStringEncoding kMediumStringEncoding = kCFStringEncodingUTF16BE;
 static const CFStringEncoding kWideStringEncoding = kCFStringEncodingUTF32BE;
-#endif  // WCHAR_T_IS_UTF32
 #elif defined(__LITTLE_ENDIAN__)
-#if defined(WCHAR_T_IS_UTF16)
-static const CFStringEncoding kWideStringEncoding = kCFStringEncodingUTF16LE;
-#elif defined(WCHAR_T_IS_UTF32)
+static const CFStringEncoding kMediumStringEncoding = kCFStringEncodingUTF16LE;
 static const CFStringEncoding kWideStringEncoding = kCFStringEncodingUTF32LE;
-#endif  // WCHAR_T_IS_UTF32
 #endif  // __LITTLE_ENDIAN__
 
 }  // namespace
 
 // Do not assert in this function since it is used by the asssertion code!
 std::string SysWideToUTF8(const std::wstring& wide) {
   return STLStringToSTLStringWithEncodingsT<std::wstring, std::string>(
       wide, kWideStringEncoding, kNarrowStringEncoding);
 }
 
 // Do not assert in this function since it is used by the asssertion code!
 std::wstring SysUTF8ToWide(const StringPiece& utf8) {
   return STLStringToSTLStringWithEncodingsT<StringPiece, std::wstring>(
       utf8, kNarrowStringEncoding, kWideStringEncoding);
 }
 
 std::string SysWideToNativeMB(const std::wstring& wide) {
   return SysWideToUTF8(wide);
 }
 
 std::wstring SysNativeMBToWide(const StringPiece& native_mb) {
   return SysUTF8ToWide(native_mb);
 }
 
 CFStringRef SysUTF8ToCFStringRef(const std::string& utf8) {
   return STLStringToCFStringWithEncodingsT(utf8, kNarrowStringEncoding);
 }
 
+CFStringRef SysUTF16ToCFStringRef(const string16& utf16) {
+  return STLStringToCFStringWithEncodingsT(utf16, kMediumStringEncoding);
+}
+
 CFStringRef SysWideToCFStringRef(const std::wstring& wide) {
   return STLStringToCFStringWithEncodingsT(wide, kWideStringEncoding);
 }
 
 NSString* SysUTF8ToNSString(const std::string& utf8) {
   return CFTypeRefToNSObjectAutorelease(SysUTF8ToCFStringRef(utf8));
 }
 
+NSString* SysUTF16ToNSString(const string16& utf16) {
+  return CFTypeRefToNSObjectAutorelease(SysUTF16ToCFStringRef(utf16));
+}
+
 NSString* SysWideToNSString(const std::wstring& wide) {
   return CFTypeRefToNSObjectAutorelease(SysWideToCFStringRef(wide));
 }
 
 std::string SysCFStringRefToUTF8(CFStringRef ref) {
   return CFStringToSTLStringWithEncodingT<std::string>(ref,
                                                        kNarrowStringEncoding);
 }
 
+string16 SysCFStringRefToUTF16(CFStringRef ref) {
+  return CFStringToSTLStringWithEncodingT<string16>(ref,
+                                                    kMediumStringEncoding);
+}
+
 std::wstring SysCFStringRefToWide(CFStringRef ref) {
   return CFStringToSTLStringWithEncodingT<std::wstring>(ref,
                                                         kWideStringEncoding);
 }
 
 std::string SysNSStringToUTF8(NSString* nsstring) {
   return SysCFStringRefToUTF8(reinterpret_cast<CFStringRef>(nsstring));
 }
 
+string16 SysNSStringToUTF16(NSString* nsstring) {
+  return SysCFStringRefToUTF16(reinterpret_cast<CFStringRef>(nsstring));
+}
+
 std::wstring SysNSStringToWide(NSString* nsstring) {
   return SysCFStringRefToWide(reinterpret_cast<CFStringRef>(nsstring));
 }
 
 }  // namespace base