Make zero-termination optional.

pkg/front_end/lib/src/fasta/io.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.io;
 
 import 'dart:async' show Future;
 
 import 'dart:io' show FileSystemException;
 
 import 'errors.dart' show inputError;
 
 import 'scanner/io.dart' as scanner_io show readBytesFromFile;
 
-Future<List<int>> readBytesFromFile(Uri uri) async {
+Future<List<int>> readBytesFromFile(Uri uri,
+    {bool ensureZeroTermination: true}) async {
   try {
-    return await scanner_io.readBytesFromFile(uri);
+    return await scanner_io.readBytesFromFile(uri,
+        ensureZeroTermination: ensureZeroTermination);
   } on FileSystemException catch (e) {
     String message = e.message;
     String osMessage = e.osError?.message;
     if (osMessage != null && osMessage.isNotEmpty) {
       message = osMessage;
     }
     return inputError(uri, -1, message);
   }
 }