Enable Null Syncable ID which is different than Root ID.

sync/syncable/directory_unittest.cc

 // Copyright 2014 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.
 
 #include "sync/syncable/directory_unittest.h"
 
 #include "base/strings/stringprintf.h"
 #include "base/test/values_test_util.h"
 #include "sync/internal_api/public/base/attachment_id_proto.h"
 #include "sync/syncable/syncable_proto_util.h"
@@ skipping 1331 matching lines @@
   const Id id = TestIdFactory::FromNumber(99);
   std::string name = "Jeff";
   {
     ReadTransaction rtrans(FROM_HERE, dir().get());
     Entry e(&rtrans, GET_BY_ID, id);
     ASSERT_FALSE(e.good());  // Hasn't been written yet.
 
     Entry root(&rtrans, GET_BY_ID, rtrans.root_id());
     ASSERT_TRUE(root.good());
     EXPECT_FALSE(dir()->HasChildren(&rtrans, rtrans.root_id()));
-    EXPECT_TRUE(root.GetFirstChildId().IsRoot());
+    EXPECT_TRUE(root.GetFirstChildId().IsNull());
   }
 
   {
     WriteTransaction wtrans(FROM_HERE, UNITTEST, dir().get());
     MutableEntry me(&wtrans, CREATE, BOOKMARKS, wtrans.root_id(), name);
     ASSERT_TRUE(me.good());
     me.PutId(id);
     me.PutBaseVersion(1);
     written_metahandle = me.GetMetahandle();
   }
@@ skipping 22 matching lines @@
 
   // Test children ops after the children have been deleted.
   {
     ReadTransaction rtrans(FROM_HERE, dir().get());
     Entry e(&rtrans, GET_BY_ID, id);
     ASSERT_TRUE(e.good());
 
     Entry root(&rtrans, GET_BY_ID, rtrans.root_id());
     ASSERT_TRUE(root.good());
     EXPECT_FALSE(dir()->HasChildren(&rtrans, rtrans.root_id()));
-    EXPECT_TRUE(root.GetFirstChildId().IsRoot());
+    EXPECT_TRUE(root.GetFirstChildId().IsNull());
   }
 
   dir()->SaveChanges();
 }
 
 TEST_F(SyncableDirectoryTest, ClientIndexRebuildsProperly) {
   int64 written_metahandle;
   TestIdFactory factory;
   const Id id = factory.NewServerId();
   std::string name = "cheesepuffs";
@@ skipping 356 matching lines @@
   {
     ReadTransaction trans(FROM_HERE, dir().get());
     dir()->GetAttachmentIdsToUpload(&trans, PREFERENCES, &id_set);
   }
   ASSERT_TRUE(id_set.empty());
 }
 
 }  // namespace syncable
 
 }  // namespace syncer