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..fd11cc2025777d4e5d9e04f657b8a7a6b85a5624 100644
--- a/sync/api/sync_change.cc
+++ b/sync/api/sync_change.cc
@@ -32,7 +32,7 @@ bool SyncChange::IsValid() const {
     return IsRealDataType(sync_data_.GetDataType());
 
   // 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;
   }