drive: Use ResourceMetadataStorage from FileCache

chrome/browser/chromeos/drive/file_cache_metadata.h

 // Copyright (c) 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 CHROME_BROWSER_CHROMEOS_DRIVE_FILE_CACHE_METADATA_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_CACHE_METADATA_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 10 matching lines @@
 class DB;
 class Iterator;
 }  // namespace leveldb
 
 namespace drive {
 namespace internal {
 
 // FileCacheMetadata maintains metadata of FileCache's cached files.
 // This class only manages metadata. File operations are done by FileCache.
 // All member access including ctor and dtor must be made on the blocking pool.
+//
+// OBSOLETE: This class is maintained only for importing old data.
+// TODO(hashimoto): Remove this class at some point.
 class FileCacheMetadata {
  public:
   // Result of Initialize().
   enum InitializeResult {
     INITIALIZE_FAILED,  // Could not open nor create DB.
     INITIALIZE_OPENED,  // Opened an existing DB.
     INITIALIZE_CREATED,  // Created a new DB.
   };
 
   // Object to iterate over entries stored in the cache metadata.
@@ skipping 59 matching lines @@
   scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
   scoped_ptr<leveldb::DB> level_db_;
 
   DISALLOW_COPY_AND_ASSIGN(FileCacheMetadata);
 };
 
 }  // namespace internal
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_CACHE_METADATA_H_