Introduce ItemPosition class for enhanced bookmarks.

components/enhanced_bookmarks/stars_position.h

Index: components/enhanced_bookmarks/stars_position.h
diff --git a/components/enhanced_bookmarks/stars_position.h b/components/enhanced_bookmarks/stars_position.h
new file mode 100644
index 0000000000000000000000000000000000000000..0645c09f8da9a59be65b49ec4beea2b0b63a8bb4
--- /dev/null
+++ b/components/enhanced_bookmarks/stars_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_STARS_POSITION_H_
+#define COMPONENTS_ENHANCED_BOOKMARKS_STARS_POSITION_H_
+
+#include <string>
+#include <vector>
+
+namespace enhanced_bookmarks {
+
+// Convenience class for generating string based relative ordering between
+// bookmark nodes.
+class StarsPosition {

[Yaron, 2014/09/05 03:52:02]

StarPosition/ItemPosition? Why is it plural?

[Rune Fevang, 2014/09/05 19:02:30]

Because it refers to the Stars name, and is stored under the key
'stars.position' (for folders). That said, I don't mind changing the name, which
do you prefer?

[Yaron, 2014/09/05 19:52:13]

It just reads weirdly to me and can be used without the notion of "Stars". I'd
say go for ItemPosition.

[Rune Fevang, 2014/09/05 20:47:08]

Done.

+ public:
+  ~StarsPosition();
+
+  // Creates a position suitable to use as a starting point.
+  static StarsPosition CreateInitialPosition();
+
+  // Creates positions relative to other positions.
+  static StarsPosition CreateBefore(const StarsPosition& other);
+  static StarsPosition CreateBetween(const StarsPosition& before,
+                                     const StarsPosition& after);
+  static StarsPosition CreateAfter(const StarsPosition& 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 StarsPosition& other);
+  bool LessThan(const StarsPosition& other);
+
+ private:
+  typedef std::vector<char> PositionVector;
+
+  StarsPosition();
+  explicit StarsPosition(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_STARS_POSITION_H_