Replace base::File wrapping with typemapping.

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.mojom;
 
 import "components/filesystem/public/interfaces/types.mojom";
+import "mojo/common/common_custom_types.mojom";
 
 // TODO(vtl): Write comments.
 interface File {
   // Flushes/closes this file; no operations may be performed on this file after
   // this. Note that any error code is strictly informational -- the close may
   // not be retried.
   [Sync]
   Close() => (FileError err);
 
   // Reads (at most) |num_bytes_to_read| from the location specified by
@@ skipping 54 matching lines @@
   // this file).
   [Sync]
   Lock() => (FileError error);
 
   // Unlocks a previously locked file.
   [Sync]
   Unlock() => (FileError error);
 
   // Returns a handle to the file for raw access.
   [Sync]
-  AsHandle() => (FileError error, handle file_handle);
+  AsHandle() => (FileError error, mojo.common.mojom.File? file_handle);
 };