mash: Add a simple, temporary preferences store.

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;
 
 import "components/filesystem/public/interfaces/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.
   Close() => (FileError err);
 
   // Reads (at most) |num_bytes_to_read| from the location specified by
   // |offset|/|whence|. On success, |bytes_read| is set to the data read.
   // TODO(vtl): Define/clarify behavior when less than |num_bytes_to_read| bytes
   // are read.
   // TODO(vtl): Clarify when (for what values of |offset|/|whence|) this
   // modifies the file position. Or maybe there should be a flag?
   Read(uint32 num_bytes_to_read, int64 offset, Whence whence)
       => (FileError error, array<uint8>? bytes_read);
 
+  // Returns the entire contents of the file as an array of bytes. The mojo
+  // equivalent of base::ReadFileToString().
+  ReadEntireFile() => (FileError error, array<uint8>? bytes_read);
+
   // Writes |bytes_to_write| to the location specified by |offset|/|whence|.
   // TODO(vtl): Clarify behavior when |num_bytes_written| is less than the size
   // of |bytes_to_write|.
   Write(array<uint8> bytes_to_write, int64 offset, Whence whence)
       => (FileError error, uint32 num_bytes_written);
 
   // Gets the current file position. On success, |position| is the current
   // offset (in bytes) from the beginning of the file).
   Tell() => (FileError error, int64 position);
 
@@ skipping 18 matching lines @@
   // 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);
 };