[Sync] Split DirectoryChangeListener for thread-safety

chrome/browser/sync/syncable/directory_change_delegate.h

 // 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.
 
-#ifndef CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_LISTENER_H_
-#define CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_LISTENER_H_
+#ifndef CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_DELEGATE_H_
+#define CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_DELEGATE_H_
 #pragma once
 
 #include "chrome/browser/sync/syncable/model_type.h"
 #include "chrome/browser/sync/syncable/syncable.h"
 
 namespace syncable {
 
 // This is an interface for listening to directory change events, triggered by
-// the releasing of the syncable transaction. The listener performs work to
+// the releasing of the syncable transaction. The delegate performs work to
 // 1. Calculate changes, depending on the source of the transaction
 //    (HandleCalculateChangesChangeEventFromSyncer/Syncapi).
 // 2. Perform final work while the transaction is held
 //    (HandleTransactionEndingChangeEvent).
 // 3. Perform any work that should be done after the transaction is released.
 //    (HandleTransactionCompleteChangeEvent).
-class DirectoryChangeListener {
+//
+// Note that these methods may be called on *any* thread.
+class DirectoryChangeDelegate {
  public:
   virtual void HandleCalculateChangesChangeEventFromSyncApi(
       const OriginalEntries& originals,
-      const WriterTag& writer,
       BaseTransaction* trans) = 0;
   virtual void HandleCalculateChangesChangeEventFromSyncer(
       const OriginalEntries& originals,
-      const WriterTag& writer,
       BaseTransaction* trans) = 0;
+  // Must return the set of all ModelTypes that were modified in the
+  // transaction.
   virtual ModelTypeBitSet HandleTransactionEndingChangeEvent(
       BaseTransaction* trans) = 0;
   virtual void HandleTransactionCompleteChangeEvent(
       const ModelTypeBitSet& models_with_changes) = 0;
  protected:
-  virtual ~DirectoryChangeListener() {}
+  virtual ~DirectoryChangeDelegate() {}
 };
 
 }  // namespace syncable
 
-#endif  // CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_LISTENER_H_
+#endif  // CHROME_BROWSER_SYNC_SYNCABLE_DIRECTORY_CHANGE_DELEGATE_H_