[Sync] Generalize StringOrdinal to handle ordinal_in_parent field

chrome/common/string_ordinal.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.
-
-#ifndef CHROME_COMMON_STRING_ORDINAL_H_
-#define CHROME_COMMON_STRING_ORDINAL_H_
-
-#include <string>
-
-// A StringOrdinal represents a specially-formatted string that can be used
-// for ordering. The StringOrdinal class has an unbounded dense strict total
-// order, which mean for any StringOrdinals a, b and c:
-//
-//  - a < b and b < c implies a < c (transitivity);
-//  - exactly one of a < b, b < a and a = b holds (trichotomy);
-//  - if a < b, there is a StringOrdinal x such that a < x < b (density);
-//  - there are StringOrdinals x and y such that x < a < y (unboundedness).
-//
-// This means that when StringOrdinal is used for sorting a list, if
-// any item changes its position in the list, only its StringOrdinal value
-// has to change to represent the new order, and all the other older values
-// can stay the same.
-class StringOrdinal {
- public:
-  // Creates a StringOrdinal from the given string. It may be valid or invalid.
-  explicit StringOrdinal(const std::string& string_ordinal);
-
-  // Creates an invalid StringOrdinal.
-  StringOrdinal();
-
-  // Creates a valid initial StringOrdinal, this is called to create the first
-  // element of StringOrdinal list (i.e. before we have any other values we can
-  // generate from).
-  static StringOrdinal CreateInitialOrdinal();
-
-  bool IsValid() const;
-
-  // All remaining functions can only be called if IsValid() holds.
-  // It is an error to call them if IsValid() is false.
-
-  // Order-related Functions
-
-  // Returns true iff |*this| < |other|.
-  bool LessThan(const StringOrdinal& other) const;
-
-  // Returns true iff |*this| > |other|.
-  bool GreaterThan(const StringOrdinal& other) const;
-
-  // Returns true iff |*this| == |other| (i.e. |*this| < |other| and
-  // |other| < |*this| are both false).
-  bool Equal(const StringOrdinal& other) const;
-
-  // Returns true iff |*this| == |other| or |*this| and |other|
-  // are both invalid.
-  bool EqualOrBothInvalid(const StringOrdinal& other) const;
-
-  // Given |*this| != |other|, returns a StringOrdinal x such that
-  // min(|*this|, |other|) < x < max(|*this|, |other|). It is an error
-  // to call this function when |*this| == |other|.
-  StringOrdinal CreateBetween(const StringOrdinal& other) const;
-
-  // Returns a StringOrdinal |x| such that |x| < |*this|.
-  StringOrdinal CreateBefore() const;
-
-  // Returns a StringOrdinal |x| such that |*this| < |x|.
-  StringOrdinal CreateAfter() const;
-
-  // It is guaranteed that a StringOrdinal constructed from the returned
-  // string will be valid.
-  std::string ToString() const;
-
-  // Do this so we can use std::find on a std::vector of StringOrdinals.
-  bool operator==(const StringOrdinal& rhs) const;
-
-  // Use of copy constructor and default assignment for this class is allowed.
-
- private:
-  // The string representation of the StringOrdinal.
-  std::string string_ordinal_;
-
-  // The validity of the StringOrdinal (i.e., is it of the format [a-z]*[b-z]),
-  // created to cache validity to prevent frequent recalculations.
-  bool is_valid_;
-};
-
-// A helper class that can be used by STL containers that require sorting.
-class StringOrdinalLessThan {
- public:
-  bool operator() (const StringOrdinal& lhs, const StringOrdinal& rhs) const;
-};
-
-#endif  // CHROME_COMMON_STRING_ORDINAL_H_