@Override
    public void visitFile(File file) {
      FileInfo info = getShardFileInfo(file);
      if (info != null && info.type == FileType.CONTENT) {
        result.add(new EntryImpl(info.resourceId, file));
      }
    }
Implementation of {@link FileTreeVisitor} to iterate over all the sharded files and collect
those valid content files. It's used in entriesIterator method.
imagepipeline-base/src/main/java/com/facebook/cache/disk/DefaultDiskStorage.java