Reland: Create hard links in file migration if necessary.

components/drive/file_cache.h

Index: components/drive/file_cache.h
diff --git a/components/drive/file_cache.h b/components/drive/file_cache.h
index c63756637923ef99e51b0405cc875bbb9c8b0499..2dad5da4d80cf8bb9f1851e868157aa6d851bbf2 100644
--- a/components/drive/file_cache.h
+++ b/components/drive/file_cache.h
@@ -157,10 +157,12 @@ class FileCache {
       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: