[Sync] Replace uses of ObserverListThreadSafe with WeakHandles

chrome/browser/sync/syncable/syncable_mock.cc

 // 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.
 
 #include "chrome/browser/sync/syncable/syncable_mock.h"
 
 #include "base/location.h"
+#include "chrome/browser/sync/test/null_transaction_observer.h"
 
 MockDirectory::MockDirectory() {
-  InitKernel("myk", &delegate_);
+  InitKernelForTest("myk", &delegate_, syncable::NullTransactionObserver());
 }
 
 MockDirectory::~MockDirectory() {}
 
 MockSyncableWriteTransaction::MockSyncableWriteTransaction(
     const tracked_objects::Location& from_here, Directory *directory)
     : WriteTransaction(from_here, syncable::UNITTEST, directory) {
 }