This directory contains part of the browser side implementation of various filesystem related APIs, as well as interfaces to treat various types of native and non-native filesystems mostly the same without having to worry about the underlying implementation.
//content/browser/fileapi/ contains the
rest of the browser side implementation, while
blink/renderer/modules/filesystem
contains the renderer side implementation and
blink/public/mojom/filesystem
contains the mojom interfaces for these APIs.