Separate SyncData methods into three groups, local, remote, and common.

sync/api/sync_change.cc

Index: sync/api/sync_change.cc
diff --git a/sync/api/sync_change.cc b/sync/api/sync_change.cc
index 8dedd9cb1768fbb0b3f99aebe8ae38e0cad773f7..4e0a8b822d04fbe7c68637d79ff886c0a66197a8 100644
--- a/sync/api/sync_change.cc
+++ b/sync/api/sync_change.cc
@@ -31,8 +31,10 @@ bool SyncChange::IsValid() const {
   if (!sync_data_.IsLocal())
     return IsRealDataType(sync_data_.GetDataType());
 
+  SyncDataLocal sync_data_local(sync_data_.AsLocal());
+
   // Local changes must always have a tag and specify a valid datatype.
-  if (sync_data_.GetTag().empty() ||
+  if (sync_data_local.GetTag().empty() ||
       !IsRealDataType(sync_data_.GetDataType())) {
     return false;
   }