arc: Create sync protos for Arc package.

components/sync_driver/user_selectable_sync_type.h

Index: components/sync_driver/user_selectable_sync_type.h
diff --git a/components/sync_driver/user_selectable_sync_type.h b/components/sync_driver/user_selectable_sync_type.h
index 42fd6e4faf81f95d0b040504c410e324c8138f99..b5234a6c40f1ae4ac2a4b5f0c11ce747fd4edfaf 100644
--- a/components/sync_driver/user_selectable_sync_type.h
+++ b/components/sync_driver/user_selectable_sync_type.h
@@ -38,6 +38,7 @@ enum UserSelectableSyncType {
 
   // The datatypes below are implicitly synced, and are not exposed via user
   // selectable checkboxes.
+  // TODO(lgcheng) ARC_PACKAGE would be selectable.
 
   // AUTOFILL_PROFILE,
   // NIGORI,
@@ -55,7 +56,8 @@ enum UserSelectableSyncType {
   // FAVICON_IMAGES,
   // FAVICON_TRACKING,
   // ARTICLE,
-  // SYNCED_NOTIFICATION_APP_INFO
+  // SYNCED_NOTIFICATION_APP_INFO,
+  // ARC_PACKAGE
 
   // Number of sync datatypes exposed to the user via checboxes in the UI.
   SELECTABLE_DATATYPE_COUNT = 11,