[Sync] Implement MemoryDumpProvider.

components/sync/base/unique_position.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 COMPONENTS_SYNC_BASE_UNIQUE_POSITION_H_
 #define COMPONENTS_SYNC_BASE_UNIQUE_POSITION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 83 matching lines @@
   std::string GetSuffixForTest() const;
 
   // Performs a lossy conversion to an int64_t position.  Positions converted to
   // and from int64_ts using this and the FromInt64 function should maintain
   // their
   // relative orderings unless the int64_t values conflict.
   int64_t ToInt64() const;
 
   bool IsValid() const;
 
+  // Returns memory usage estimate.
+  size_t EstimateMemoryUsage() const;
+
  private:
   friend class UniquePositionTest;
 
   // Returns a string X such that (X ++ |suffix|) < |str|.
   // |str| must be a trailing substring of a valid ordinal.
   // |suffix| must be a valid unique suffix.
   static std::string FindSmallerWithSuffix(const std::string& str,
                                            const std::string& suffix);
   // Returns a string X such that (X ++ |suffix|) > |str|.
   // |str| must be a trailing substring of a valid ordinal.
@@ skipping 22 matching lines @@
 
   // The position value after it has been run through the custom compression
   // algorithm.  See Compress() and Uncompress() functions above.
   std::string compressed_;
   bool is_valid_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_BASE_UNIQUE_POSITION_H_