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

sync/internal_api/base_node.cc

Index: sync/internal_api/base_node.cc
diff --git a/sync/internal_api/base_node.cc b/sync/internal_api/base_node.cc
index 078839540e3e66c4a9bfeb5ccd32646fa86410b6..57dbb22f72115e58dd8221f769afe2baf78bf5fc 100644
--- a/sync/internal_api/base_node.cc
+++ b/sync/internal_api/base_node.cc
@@ -291,10 +291,13 @@ ModelType BaseNode::GetModelType() const {
 }
 
 const syncer::AttachmentIdList BaseNode::GetAttachmentIds() const {
-  // TODO(maniscalco): Once EntryKernel is capable of storing AttachmentIds,
-  // update this method to retrieve the list of AttachmentIds from read_node and
-  // pass it to CreateRemoteData (bug 348625).
-  return AttachmentIdList();
+  AttachmentIdList result;
+  const sync_pb::AttachmentMetadata& metadata =
+      GetEntry()->GetAttachmentMetadata();
+  for (int i = 0; i < metadata.record_size(); ++i) {
+    result.push_back(AttachmentId::CreateFromProto(metadata.record(i).id()));
+  }
+  return result;
 }
 
 void BaseNode::SetUnencryptedSpecifics(