sync: Implementation of Priority Preferences.

sync/syncable/model_type.cc

Index: sync/syncable/model_type.cc
diff --git a/sync/syncable/model_type.cc b/sync/syncable/model_type.cc
index ba7a7f01360610ebfa297edfcab50708d052b518..b518ef95ed4df6f1526db0dc8aaaa26aa287078a 100644
--- a/sync/syncable/model_type.cc
+++ b/sync/syncable/model_type.cc
@@ -351,6 +351,9 @@ ModelTypeSet EncryptableUserTypes() {
   encryptable_user_types.Remove(HISTORY_DELETE_DIRECTIVES);
   // Synced notifications are not encrypted since the server must see changes.
   encryptable_user_types.Remove(SYNCED_NOTIFICATIONS);
+  // Priority preferences are not encrypted because they might be synced before
+  // encryption is ready.
+  encryptable_user_types.RemoveAll(PriorityUserTypes());
   // Proxy types have no sync representation and are therefore not encrypted.
   // Note however that proxy types map to one or more protocol types, which
   // may or may not be encrypted themselves.
@@ -358,6 +361,10 @@ ModelTypeSet EncryptableUserTypes() {
   return encryptable_user_types;
 }
 
+ModelTypeSet PriorityUserTypes() {
+  return ModelTypeSet(PRIORITY_PREFERENCES);
+}
+
 ModelTypeSet ControlTypes() {
   ModelTypeSet set;
   // TODO(sync): We should be able to build the actual enumset's internal
@@ -367,9 +374,6 @@ ModelTypeSet ControlTypes() {
     set.Put(ModelTypeFromInt(i));
   }
 
-  // TODO(albertb): Re-enable this when the server supports it.
-  set.Remove(PRIORITY_PREFERENCES);
-
   return set;
 }