[WIP][tracing] Add memory dump provider for sync Directory

sync/internal_api/public/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 SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 77 matching lines @@
 
   // Serializes the protobuf representation of this object as a string.
   void SerializeToString(std::string* blob) const;
 
   // Returns a human-readable representation of this item's internal state.
   std::string ToDebugString() const;
 
   // Returns the suffix.
   std::string GetSuffixForTest() const;
 
+  size_t compressed_byte_size() const { return compressed_.capacity() + 1; }
+
   // 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;
 
  private:
   friend class UniquePositionTest;
@@ skipping 30 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  // SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_