mandoline filesystem: add a sqlite3 vfs to proxy filesystem usage.

components/filesystem/public/interfaces/file.mojom

 // Copyright 2015 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.
 
 // TODO(vtl): notes to self:
 //  - file offsets, file positions, and file sizes are int64 (though positions
 //    and sizes must always be non-negative)
 //  - buffer size parameters (for read/write) are uint32
 
 module filesystem;
@@ skipping 41 matching lines @@
   // Updates this file's atime and/or mtime to the time specified by |atime| (or
   // |mtime|, respectively), which may also indicate "now". If |atime| or
   // |mtime| is null, then the corresponding time is not modified.
   Touch(TimespecOrNow? atime, TimespecOrNow? mtime) => (FileError error);
 
   // Creates a new |File| instance, which shares the same "file description".
   // I.e., the access mode, etc. (as specified to |Directory::OpenFile()| by the
   // |open_flags| argument) as well as file position.
   Dup(File& file) => (FileError error);
 
+  // Syncs data to disk.
+  Flush() => (FileError error);
+
   // Returns a handle to the file for raw access.
   AsHandle() => (FileError error, handle file_handle);
 };