Use SNAPSHOT sync mode for LocalSync

chrome/browser/sync_file_system/local/local_file_change_tracker.h

 // Copyright 2013 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_FILE_SYSTEM_LOCAL_LOCAL_FILE_CHANGE_TRACKER_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_LOCAL_FILE_CHANGE_TRACKER_H_
 
 #include <deque>
 #include <map>
 #include <string>
@@ skipping 85 matching lines @@
     return num_changes_;
   }
 
   void UpdateNumChanges();
 
  private:
   class TrackerDB;
   friend class CannedSyncableFileSystem;
   friend class LocalFileChangeTrackerTest;
   friend class LocalFileSyncContext;
+  friend class LocalFileSyncContextTest;
   friend class SyncableFileSystemTest;
 
   struct ChangeInfo {
     ChangeInfo();
     ~ChangeInfo();
     FileChangeList change_list;
     int64 change_seq;
   };
 
   typedef std::map<fileapi::FileSystemURL, ChangeInfo,
@@ skipping 44 matching lines @@
   // This can be accessed on any threads (with num_changes_lock_).
   int64 num_changes_;
   mutable base::Lock num_changes_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalFileChangeTracker);
 };
 
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_LOCAL_FILE_CHANGE_TRACKER_H_