Add new SplitString backend.

base/strings/string_piece.h

 // 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.
 // Copied from strings/stringpiece.h with modifications
 //
 // A string-like object that points to a sized piece of memory.
 //
 // You can use StringPiece as a function or method parameter.  A StringPiece
 // parameter can receive a double-quoted string literal argument, a "const
 // char*" argument, a string argument, or a StringPiece argument with no data
 // copying.  Systematic use of StringPiece for arguments reduces data
 // copies and strlen() calls.
 //
 // Prefer passing StringPieces by value:
 //   void MyFunction(StringPiece arg);
 // If circumstances require, you may also pass by const reference:
 //   void MyFunction(const StringPiece& arg);  // not preferred
 // Both of these have the same lifetime semantics.  Passing by value
 // generates slightly smaller code.  For more discussion, Googlers can see
 // the thread go/stringpiecebyvalue on c-users.
-//
-// StringPiece16 is similar to StringPiece but for base::string16 instead of
-// std::string. We do not define as large of a subset of the STL functions
-// from basic_string as in StringPiece, but this can be changed if these
-// functions (find, find_first_of, etc.) are found to be useful in this context.
-//
 
 #ifndef BASE_STRINGS_STRING_PIECE_H_
 #define BASE_STRINGS_STRING_PIECE_H_
 
 #include <stddef.h>
 
 #include <iosfwd>
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 412 matching lines @@
 template<>
 struct hash<base::StringPiece16> {
   std::size_t operator()(const base::StringPiece16& sp16) const {
     HASH_STRING_PIECE(base::StringPiece16, sp16);
   }
 };
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // BASE_STRINGS_STRING_PIECE_H_