Implement part-of directive.

dart/lib/compiler/implementation/tree/nodes.dart

 // Copyright (c) 2012, 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.
 
 abstract class Visitor<R> {
   const Visitor();
 
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
@@ skipping 36 matching lines @@
   R visitLoop(Loop node) => visitStatement(node);
   R visitModifiers(Modifiers node) => visitNode(node);
   R visitNamedArgument(NamedArgument node) => visitExpression(node);
   R visitNewExpression(NewExpression node) => visitExpression(node);
   R visitNodeList(NodeList node) => visitNode(node);
   R visitOperator(Operator node) => visitIdentifier(node);
   R visitParenthesizedExpression(ParenthesizedExpression node) {
     return visitExpression(node);
   }
   R visitPart(Part node) => visitLibraryTag(node);
-  R visitPartOf(PartOf node) => visitLibraryTag(node);
+  R visitPartOf(PartOf node) => visitNode(node);
   R visitPostfix(Postfix node) => visitNodeList(node);
   R visitPrefix(Prefix node) => visitNodeList(node);
   R visitReturn(Return node) => visitStatement(node);
   R visitScriptTag(ScriptTag node) => visitNode(node);
   R visitSend(Send node) => visitExpression(node);
   R visitSendSet(SendSet node) => visitSend(node);
   R visitStatement(Statement node) => visitNode(node);
   R visitStringNode(StringNode node) => visitExpression(node);
   R visitStringInterpolation(StringInterpolation node) => visitStringNode(node);
   R visitStringInterpolationPart(StringInterpolationPart node) {
@@ skipping 1684 matching lines @@
 
   accept(Visitor visitor) => visitor.visitPart(this);
 
   visitChildren(Visitor visitor) => uri.accept(visitor);
 
   Token getBeginToken() => partKeyword;
 
   Token getEndToken() => uri.getEndToken().next;
 }
 
-class PartOf extends LibraryTag {
+class PartOf extends Node {
   final Expression name;
 
   final Token partKeyword;
 
   PartOf(this.partKeyword, this.name);
 
   Token get ofKeyword => partKeyword.next;
 
   bool get isPartOf => true;
 
@@ skipping 204 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }