Keep track of which attachments are referenced by which sync entries.

sync/syncable/mutable_entry.h

 // Copyright 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_SYNCABLE_MUTABLE_ENTRY_H_
 #define SYNC_SYNCABLE_MUTABLE_ENTRY_H_
 
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/syncable/entry.h"
@@ skipping 41 matching lines @@
   void PutNonUniqueName(const std::string& value);
   void PutSpecifics(const sync_pb::EntitySpecifics& value);
   void PutUniquePosition(const UniquePosition& value);
 
   // Sets the position of this item, and updates the entry kernels of the
   // adjacent siblings so that list invariants are maintained.  Returns false
   // and fails if |predecessor_id| does not identify a sibling.  Pass the root
   // ID to put the node in first position.
   bool PutPredecessor(const Id& predecessor_id);
 
+  void PutAttachmentMetadata(
+      const sync_pb::AttachmentMetadata& attachment_metadata);
+
  private:
   // Kind of redundant. We should reduce the number of pointers
   // floating around if at all possible. Could we store this in Directory?
   // Scope: Set on construction, never changed after that.
   WriteTransaction* const write_transaction_;
 
   DISALLOW_COPY_AND_ASSIGN(MutableEntry);
 };
 
 // This function sets only the flags needed to get this entry to sync.
 bool MarkForSyncing(syncable::MutableEntry* e);
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_MUTABLE_ENTRY_H_