Add AttachmentMetadata to Sync's EntryKernel.

sync/syncable/syncable_columns.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_SYNCABLE_SYNCABLE_COLUMNS_H_
 #define SYNC_SYNCABLE_SYNCABLE_COLUMNS_H_
 
 #include "sync/syncable/entry_kernel.h"
 #include "sync/syncable/syncable_changes_version.h"
 
@@ skipping 43 matching lines @@
   {"unique_bookmark_tag", "varchar"},
   //////////////////////////////////////
   // Blobs (serialized protos).
   {"specifics", "blob"},
   {"server_specifics", "blob"},
   {"base_server_specifics", "blob"},
   //////////////////////////////////////
   // Blobs (positions).
   {"server_unique_position", "blob"},
   {"unique_position", "blob"},
+  //////////////////////////////////////
+  // AttachmentMetadata is a proto that contains all the metadata associated
+  // with an entry's attachments.  Each entry has only one AttachmentMetadata
+  // proto.  We store a single proto per entry (as opposed to one for each
+  // attachment) because it simplifies the database schema and implementation of
+  // DirectoryBackingStore.
+  {"attachment_metadata", "blob"}
 };
 
 // At least enforce that there are equal number of column names and fields.
 COMPILE_ASSERT(arraysize(g_metas_columns) >= FIELD_COUNT, missing_column_name);
 COMPILE_ASSERT(arraysize(g_metas_columns) <= FIELD_COUNT, extra_column_names);
 
 static inline const char* ColumnName(int field) {
   DCHECK(field < BEGIN_TEMPS);
   return g_metas_columns[field].name;
 }
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_SYNCABLE_COLUMNS_H_