[Sync] Erase sync DB when corrupted

sync/syncable/on_disk_directory_backing_store.h

 // 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.
 
 #ifndef SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 #define SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 
 #include "base/files/file_path.h"
 #include "sync/base/sync_export.h"
 #include "sync/syncable/directory_backing_store.h"
@@ skipping 22 matching lines @@
   const base::FilePath& backing_file_path() const;
 
  private:
   // A helper function that will make one attempt to load the directory.
   // Unlike Load(), it does not attempt to recover from failure.
   DirOpenResult TryLoad(Directory::MetahandlesMap* handles_map,
                         JournalIndex* delete_journals,
                         MetahandleSet* metahandles_to_purge,
                         Directory::KernelLoadInfo* kernel_load_info);
 
-  bool allow_failure_for_test_;
-  base::FilePath backing_file_path_;
+  // The path to the sync DB.
+  const base::FilePath backing_file_path_;
 
   DISALLOW_COPY_AND_ASSIGN(OnDiskDirectoryBackingStore);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_