Use messages for (some) public API errors

pkg/front_end/tool/perf.dart

 // Copyright (c) 2016, 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.
 
 /// An entrypoint used to run portions of front_end and measure its performance.
 library front_end.tool.perf;
 
 import 'dart:async';
 import 'dart:io' show Directory, File, Platform, exit;
 
@@ skipping 184 matching lines @@
 }
 
 void _reportErrors(List errors, ErrorHandler onError) {
   if (onError == null) return;
   for (var error in errors) {
     onError(new _DartkError(error));
   }
 }
 
 class _DartkError implements CompilationError {
-  String get correction => null;
+  String get tip => null;
   SourceSpan get span => null;
   final String message;
   _DartkError(this.message);
 }
 
 /// Generates unlinkmed summaries for all files in [files], and returns them in
 /// an [_UnlinkedSummaries] container.
 _UnlinkedSummaries generateUnlinkedSummaries(Set<Source> files) {
   var unlinkedSummaries = new _UnlinkedSummaries();
   for (var source in files) {
@@ skipping 215 matching lines @@
 class _Scanner extends Scanner {
   _Scanner(String contents) : super.create(new CharSequenceReader(contents)) {
     preserveComments = false;
   }
 
   @override
   void reportError(errorCode, int offset, List<Object> arguments) {
     // ignore errors.
   }
 }