[Sync] Split DirectoryChangeListener for thread-safety

chrome/browser/sync/engine/syncapi.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.
 
 // This file defines the "sync API", an interface to the syncer
 // backend that exposes (1) the core functionality of maintaining a consistent
 // local snapshot of a hierarchical object set; (2) a means to transactionally
 // access and modify those objects; (3) a means to control client/server
 // synchronization tasks, namely: pushing local object modifications to a
 // server, pulling nonlocal object modifications from a server to this client,
@@ skipping 526 matching lines @@
 
  private:
   // A syncable ScopedDirLookup, which is the parent of syncable transactions.
   syncable::ScopedDirLookup* lookup_;
 
   browser_sync::Cryptographer* cryptographer_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseTransaction);
 };
 
+// TODO(akalin): Make ReadTransaction/WriteTransaction take a Location
+// parameter.
+
 // Sync API's ReadTransaction is a read-only BaseTransaction.  It wraps
 // a syncable::ReadTransaction.
 class ReadTransaction : public BaseTransaction {
  public:
   // Start a new read-only transaction on the specified repository.
   explicit ReadTransaction(UserShare* share);
 
   // Resume the middle of a transaction. Will not close transaction.
   ReadTransaction(UserShare* share, syncable::BaseTransaction* trans);
 
@@ skipping 504 matching lines @@
  private:
   // An opaque pointer to the nested private class.
   SyncInternal* data_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncManager);
 };
 
 }  // namespace sync_api
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_SYNCAPI_H_