sync: Introduce control data types

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 83e803cdd58c451f6b8eae1efa8e35e56e156203..17af4adcaad7f6e34ed908d5462095445d4f0e2d 100644
--- a/sync/syncable/model_type.cc
+++ b/sync/syncable/model_type.cc
@@ -226,6 +226,26 @@ bool ShouldMaintainPosition(ModelType model_type) {
   return model_type == BOOKMARKS;
 }
 
+ModelTypeSet UserTypes() {
+  ModelTypeSet set;
+  for (int i = FIRST_USER_MODEL_TYPE; i <= LAST_USER_MODEL_TYPE; ++i) {
+    set.Put(ModelTypeFromInt(i));
+  }
+  return set;
+}
+
+ModelTypeSet ControlTypes() {
+  ModelTypeSet set;
+  for (int i = FIRST_CONTROL_MODEL_TYPE; i <= LAST_CONTROL_MODEL_TYPE; ++i) {
+    set.Put(ModelTypeFromInt(i));
+  }
+  return set;
+}
+
+bool IsControlType(ModelType model_type) {
+  return ControlTypes().Has(model_type);
+}
+
 const char* ModelTypeToString(ModelType model_type) {
   // This is used in serialization routines as well as for displaying debug
   // information.  Do not attempt to change these string values unless you know