Add AttachmentMetadata to Sync's EntryKernel.

sync/syncable/directory_backing_store.cc

Index: sync/syncable/directory_backing_store.cc
diff --git a/sync/syncable/directory_backing_store.cc b/sync/syncable/directory_backing_store.cc
index 417a4d10e3363a7630d1352ea9050f550f957e5f..5371f43b2a62e110b6681c91cf55f4d80b5adf53 100644
--- a/sync/syncable/directory_backing_store.cc
+++ b/sync/syncable/directory_backing_store.cc
@@ -35,7 +35,7 @@ namespace syncable {
 static const string::size_type kUpdateStatementBufferSize = 2048;
 
 // Increment this version whenever updating DB tables.
-const int32 kCurrentDBVersion = 86;
+const int32 kCurrentDBVersion = 87;
 
 // Iterate over the fields of |entry| and bind each to |statement| for
 // updating.  Returns the number of args bound.
@@ -406,6 +406,12 @@ bool DirectoryBackingStore::InitializeTables() {
       version_on_disk = 86;
   }
 
+  // Version 87 migration adds a collection of attachment ids per sync entry.
+  if (version_on_disk == 86) {
+    if (MigrateVersion86To87())
+      version_on_disk = 87;
+  }
+
   // If one of the migrations requested it, drop columns that aren't current.
   // It's only safe to do this after migrating all the way to the current
   // version.
@@ -1266,6 +1272,18 @@ bool DirectoryBackingStore::MigrateVersion85To86() {
   return true;
 }
 
+bool DirectoryBackingStore::MigrateVersion86To87() {
+  // Version 87 adds AttachmentMetadata proto.
+  if (!db_->Execute(
+          "ALTER TABLE metas ADD COLUMN "
+          "attachment_metadata BLOB")) {
+    return false;
+  }
+  SetVersion(87);
+  needs_column_refresh_ = true;
+  return true;
+}
+
 bool DirectoryBackingStore::CreateTables() {
   DVLOG(1) << "First run, creating tables";
   // Create two little tables share_version and share_info