Report messages instead of just printing.

pkg/front_end/lib/src/base/processed_options.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.
 
 import 'dart:async';
 
 import 'package:front_end/compilation_error.dart';
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/base/performace_logger.dart';
@@ skipping 95 matching lines @@
   /// The logger to report compilation progress.
   PerformanceLog get logger {
     return _raw.logger;
   }
 
   /// The byte storage to get and put serialized data.
   ByteStore get byteStore {
     return _raw.byteStore;
   }
 
-  // TODO(sigmund,ahe): delete in favor of reportMessage.
-  void deprecated_reportError(String error) {
-    _raw.onError(new _StringMessage(error));
-  }
-
   void reportMessage(LocatedMessage message) {
     _raw.onError(new _CompilationMessage(message));
   }
 
   void reportMessageWithoutLocation(Message message) =>
       reportMessage(message.withLocation(null, -1));
 
   /// Runs various validations checks on the input options. For instance,
   /// if an option is a path to a file, it checks that the file exists.
   Future<bool> validateOptions() async {
@@ skipping 236 matching lines @@
   String get tip => original.tip;
 
   SourceSpan get span =>
       new SourceLocation(original.charOffset, sourceUrl: original.uri)
           .pointSpan();
 
   _CompilationMessage(this.original);
 
   String toString() => message;
 }
-
-/// Wraps an error message as a [CompilationError] API.
-class _StringMessage implements CompilationError {
-  final String message;
-  String get tip => null;
-  SourceSpan get span => null;
-
-  _StringMessage(this.message);
-
-  String toString() => message;
-}