Enable sync for the settings from the Extension Settings API.

chrome/browser/sync/syncable/model_type.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Enumerate the various item subtypes that are supported by sync.
 // Each sync object is expected to have an immutable object type.
 // An object's type is inferred from the type of data it holds.
 
 #ifndef CHROME_BROWSER_SYNC_SYNCABLE_MODEL_TYPE_H_
 #define CHROME_BROWSER_SYNC_SYNCABLE_MODEL_TYPE_H_
@@ skipping 56 matching lines @@
   // An extension folder or an extension object.
   EXTENSIONS,
   // An object representing a set of Nigori keys.
   NIGORI,
   // An object representing a custom search engine.
   SEARCH_ENGINES,
   // An object representing a browser session.
   SESSIONS,
   // An app folder or an app object.
   APPS,
+  // A setting from the extension settings API.
+  EXTENSION_SETTINGS,
 
   MODEL_TYPE_COUNT,
 };
 
 typedef std::bitset<MODEL_TYPE_COUNT> ModelTypeBitSet;
 typedef std::set<ModelType> ModelTypeSet;
 
 inline ModelType ModelTypeFromInt(int i) {
   DCHECK_GE(i, 0);
   DCHECK_LT(i, MODEL_TYPE_COUNT);
@@ skipping 81 matching lines @@
 
 // Returns a ModelTypeSet with all real model types.
 ModelTypeSet GetAllRealModelTypes();
 
 // Returns true if |model_type| is a real datatype
 bool IsRealDataType(ModelType model_type);
 
 }  // namespace syncable
 
 #endif  // CHROME_BROWSER_SYNC_SYNCABLE_MODEL_TYPE_H_