Introduce ItemPosition class for enhanced bookmarks.

components/enhanced_bookmarks/item_position.h

Index: components/enhanced_bookmarks/item_position.h
diff --git a/components/enhanced_bookmarks/item_position.h b/components/enhanced_bookmarks/item_position.h
new file mode 100644
index 0000000000000000000000000000000000000000..ea04be59355ffa7f1ff09d267b51ca6804d39644
--- /dev/null
+++ b/components/enhanced_bookmarks/item_position.h
@@ -0,0 +1,57 @@
+// Copyright 2014 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 COMPONENTS_ENHANCED_BOOKMARKS_ITEM_POSITION_H_
+#define COMPONENTS_ENHANCED_BOOKMARKS_ITEM_POSITION_H_
+
+#include <string>
+#include <vector>
+
+namespace enhanced_bookmarks {
+
+// Convenience class for generating string based relative ordering between
+// bookmark nodes.
+class ItemPosition {
+ public:
+  ~ItemPosition();
+
+  // Creates a position suitable to use as a starting point.
+  static ItemPosition CreateInitialPosition();
+
+  // Creates positions relative to other positions.
+  static ItemPosition CreateBefore(const ItemPosition& other);
+  static ItemPosition CreateBetween(const ItemPosition& before,
+                                    const ItemPosition& after);
+  static ItemPosition CreateAfter(const ItemPosition& other);
+
+  bool IsValid() const;
+
+  // Returns a string representation of the position. The string representations
+  // of two position have the same ordering as the positions themselves when
+  // compared using ASCII order.
+  std::string ToString() const;
+
+  // Comparison functions.
+  bool Equals(const ItemPosition& other) const;
+  bool LessThan(const ItemPosition& other) const;
+
+ private:
+  typedef std::vector<unsigned char> PositionVector;
+
+  ItemPosition();
+  explicit ItemPosition(const PositionVector& position);
+
+  static PositionVector CreateBeforeImpl(const PositionVector& before,
+                                         size_t from_index);
+  static PositionVector CreateBetweenImpl(const PositionVector& before,
+                                          const PositionVector& after);
+  static PositionVector CreateAfterImpl(const PositionVector& after,
+                                        size_t from_index);
+
+  PositionVector position_;
+};
+
+}  // namespace enhanced_bookmarks
+
+#endif  // COMPONENTS_ENHANCED_BOOKMARKS_ITEM_POSITION_H_