Reland: Create hard links in file migration if necessary.

components/drive/file_cache.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 COMPONENTS_DRIVE_FILE_CACHE_H_
 #define COMPONENTS_DRIVE_FILE_CACHE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 139 matching lines @@
 
   // Moves files in the cache directory which are not managed by FileCache to
   // |dest_directory|.
   // |recovered_cache_info| should contain cache info recovered from the trashed
   // metadata DB. It is used to ignore non-dirty files.
   bool RecoverFilesFromCacheDirectory(
       const base::FilePath& dest_directory,
       const ResourceMetadataStorage::RecoveredCacheInfoMap&
           recovered_cache_info);
 
-  // Migrates cache files from |from| directory to |to| directory. Returns true
-  // for success.
+  // Migrates cache files from |from| directory to |to_files| directory with
+  // creating links in |to_links| directory if necessary. Returns true for
+  // success.
   static bool MigrateCacheFiles(const base::FilePath& from,
-                                const base::FilePath& to,
+                                const base::FilePath& to_files,
+                                const base::FilePath& to_links,
                                 ResourceMetadataStorage* metadata_storage);
 
  private:
   friend class FileCacheTest;
 
   ~FileCache();
 
   // Returns absolute path of the file if it were cached or to be cached.
   //
   // Can be called on any thread.
@@ skipping 48 matching lines @@
   // invalidate its weak pointers before any other members are destroyed.
   // This object should be accessed only on |blocking_task_runner_|.
   base::WeakPtrFactory<FileCache> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(FileCache);
 };
 
 }  // namespace internal
 }  // namespace drive
 
 #endif  // COMPONENTS_DRIVE_FILE_CACHE_H_