Enable Null Syncable ID which is different than Root ID.

sync/engine/syncer_unittest.cc

 // Copyright 2012 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.
 //
 // Syncer unit tests. Unfortunately a lot of these tests
 // are outdated and need to be reworked and updated.
 
 #include <algorithm>
 #include <limits>
 #include <list>
@@ skipping 4661 matching lines @@
 TEST_F(SyncerBookmarksTest, LocalDeleteRemoteChangeConflict) {
   Create();
   ExpectUnsyncedCreation();
   SyncShareNudge();
   ExpectSyncedAndCreated();
   Delete();
   ExpectUnsyncedDeletion();
 
   // Trigger a getupdates that modifies the bookmark. The update should  be
   // clobbered by the local delete.
-  mock_server_->AddUpdateBookmark(GetServerId(), Id(), "dummy", 10, 10,
+  mock_server_->AddUpdateBookmark(GetServerId(), Id::GetRoot(), "dummy", 10, 10,
                                   local_cache_guid(), local_id_.GetServerId());
 
   SyncShareNudge();
   ExpectSyncedAndDeleted();
 }
 
 TEST_F(SyncerBookmarksTest, CreateThenDeleteDuringCommit) {
   Create();
   ExpectUnsyncedCreation();
 
@@ skipping 591 matching lines @@
     EXPECT_EQ("xyz", final_monitor_records["xyz"].extension_id);
     EXPECT_EQ(2049U, final_monitor_records["ABC"].bookmark_write_count);
     EXPECT_EQ(4U,    final_monitor_records["xyz"].bookmark_write_count);
   } else {
     EXPECT_TRUE(final_monitor_records.empty())
         << "Should not restore records after successful bookmark commit.";
   }
 }
 
 }  // namespace syncer