sync: Specialize functions that fetch type root

sync/syncable/entry.h

Index: sync/syncable/entry.h
diff --git a/sync/syncable/entry.h b/sync/syncable/entry.h
index 47b9c593301d0d96f88aefef8f4f9f7d5d80a6b1..619c84bb8280bba5d6bcd9059d325527eb4c15d0 100644
--- a/sync/syncable/entry.h
+++ b/sync/syncable/entry.h
@@ -35,9 +35,14 @@ enum GetByClientTag {
 };
 
 enum GetByServerTag {
+  // Server tagged items are deprecated for all types but bookmarks.
   GET_BY_SERVER_TAG
 };
 
+enum GetTypeRoot {
+  GET_TYPE_ROOT
+};
+
 enum GetByHandle {
   GET_BY_HANDLE
 };
@@ -48,9 +53,13 @@ class SYNC_EXPORT Entry {
   // succeeded.
   Entry(BaseTransaction* trans, GetByHandle, int64 handle);
   Entry(BaseTransaction* trans, GetById, const Id& id);
-  Entry(BaseTransaction* trans, GetByServerTag, const std::string& tag);
+  Entry(BaseTransaction* trans, GetTypeRoot, ModelType type);
   Entry(BaseTransaction* trans, GetByClientTag, const std::string& tag);
 
+  // This lookup function is deprecated.  All types except bookmarks can use
+  // the GetTypeRoot variant instead.
+  Entry(BaseTransaction* trans, GetByServerTag, const std::string& tag);
+
   bool good() const { return 0 != kernel_; }
 
   BaseTransaction* trans() const { return basetrans_; }