Reject deprecated language features.

dart/sdk/lib/_internal/compiler/implementation/util/util.dart

 // Copyright (c) 2011, 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 org_dartlang_compiler_util;
 
 import 'util_implementation.dart';
 import 'characters.dart';
 
 part 'link.dart';
 
 /**
  * Tagging interface for classes from which source spans can be generated.
  */
 // TODO(johnniwinther): Find a better name.
 // TODO(ahe): How about "Bolt"?
 abstract class Spannable {}
 
 class SpannableAssertionFailure {
   final Spannable node;
   final String message;
   SpannableAssertionFailure(this.node, this.message);
 
-  String toString() => 'compiler crashed.';
+  String toString() => 'Compiler crashed: $message.';
 }
 
 /// Writes the characters of [iterator] on [buffer].  The characters
 /// are escaped as suitable for JavaScript and JSON.  [buffer] is
 /// anything which supports [:add:] and [:addCharCode:], for example,
 /// [StringBuffer].
 void writeJsonEscapedCharsOn(Iterator<int> iterator, buffer, onError(code)) {
   while (iterator.hasNext) {
     int code = iterator.next();
     if (identical(code, $SQ)) {
@@ skipping 31 matching lines @@
             buffer.add('0');
           }
         }
         buffer.add(code.toRadixString(16));
       } else {
         buffer.addCharCode(code);
       }
     }
   }
 }