Defer to engine for option-aware context config.

lib/src/options.dart

 // Copyright (c) 2015, 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 analyzer_cli.src.options;
 
 import 'dart:io';
 
+import 'package:analyzer_cli/src/driver.dart';
 import 'package:args/args.dart';
 import 'package:cli_util/cli_util.dart' show getSdkDir;
 
 const _binaryName = 'dartanalyzer';
 
 /// Shared exit handler.
 ///
 /// *Visible for testing.*
 ExitHandler exitHandler = exit;
 
 /// Print the given message to stderr and exit with the given [exitCode]
 void printAndFail(String message, {int exitCode: 15}) {
-  stderr.writeln(message);
+  errorSink.writeln(message);
   exitHandler(exitCode);
 }
 
 /// Exit handler.
 ///
 /// *Visible for testing.*
 typedef void ExitHandler(int code);
 
 /// Analyzer commandline configuration options.
 class CommandLineOptions {
@@ skipping 452 matching lines @@
 
   int _getNextFlagIndex(args, i) {
     for (; i < args.length; ++i) {
       if (args[i].startsWith('--')) {
         return i;
       }
     }
     return i;
   }
 }