Add a mojo struct corresponding and typemapped to base::File.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 300 matching lines @@
     "file_descriptor_posix.h",
     "file_version_info.h",
     "file_version_info_mac.h",
     "file_version_info_mac.mm",
     "file_version_info_win.cc",
     "file_version_info_win.h",
     "files/dir_reader_fallback.h",
     "files/dir_reader_linux.h",
     "files/dir_reader_posix.h",
     "files/file.cc",
+    "files/file.h",
     "files/file_descriptor_watcher_posix.cc",
     "files/file_descriptor_watcher_posix.h",
     "files/file_enumerator.cc",
     "files/file_enumerator.h",
     "files/file_enumerator_posix.cc",
     "files/file_enumerator_win.cc",
     "files/file_path.cc",
     "files/file_path.h",
     "files/file_path_constants.cc",
     "files/file_path_watcher.cc",
@@ skipping 2171 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }