Formatter workaround for missing abstract keyword in ClassTypeAliases (dartbug.com/15912).

pkg/analyzer/lib/src/services/formatter_impl.dart

 // Copyright (c) 2013, 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 formatter_impl;
 
 import 'dart:math';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/java_core.dart' show CharSequence;
@@ skipping 498 matching lines @@
     });
     token(node.leftBracket);
     indent();
     visitNodes(node.members, precededBy: newlines, separatedBy: newlines);
     unindent();
     newlines();
     token(node.rightBracket);
   }
 
   visitClassTypeAlias(ClassTypeAlias node) {
+    preserveLeadingNewlines();
+    //TODO(pquitslund): the following _should_ work (dartbug.com/15912)
+    //modifier(node.abstractKeyword);
+    // ... in the meantime we use this workaround
+    var prev = node.keyword.previous;
+    if (prev.keyword == Keyword.ABSTRACT) {
+      token(prev);
+      space();
+    }
     token(node.keyword);
     space();
     visit(node.name);
     visit(node.typeParameters);
     space();
     token(node.equals);
     space();
-    if (node.abstractKeyword != null) {
-      token(node.abstractKeyword);
-      space();
-    }
     visit(node.superclass);
     visitNode(node.withClause, precededBy: space);
     visitNode(node.implementsClause, precededBy: space);
     token(node.semicolon);
   }
 
   visitComment(Comment node) => null;
 
   visitCommentReference(CommentReference node) => null;
 
@@ skipping 1088 matching lines @@
     var lastLine =
         lineInfo.getLocation(lastOffset).lineNumber;
     var currentLine =
         lineInfo.getLocation(currentOffset).lineNumber;
     return currentLine - lastLine;
   }
 
   String toString() => writer.toString();
 
 }