Add LibraryDependencyMirror+CombinatorMirror to source mirrors.

sdk/lib/_internal/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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 144 matching lines @@
   For asFor() => null;
   ForIn asForIn() => null;
   FunctionDeclaration asFunctionDeclaration() => null;
   FunctionExpression asFunctionExpression() => null;
   Identifier asIdentifier() => null;
   If asIf() => null;
   Import asImport() => null;
   Label asLabel() => null;
   LabeledStatement asLabeledStatement() => null;
   LibraryName asLibraryName() => null;
+  LibraryDependency asLibraryDependency() => null;
   LiteralBool asLiteralBool() => null;
   LiteralDouble asLiteralDouble() => null;
   LiteralInt asLiteralInt() => null;
   LiteralList asLiteralList() => null;
   LiteralMap asLiteralMap() => null;
   LiteralMapEntry asLiteralMapEntry() => null;
   LiteralNull asLiteralNull() => null;
   LiteralString asLiteralString() => null;
   MixinApplication asMixinApplication() => null;
   Modifiers asModifiers() => null;
@@ skipping 1595 matching lines @@
  * Combinators filter away some identifiers from the other library.
  */
 abstract class LibraryDependency extends LibraryTag {
   final StringNode uri;
   final NodeList combinators;
 
   LibraryDependency(this.uri,
                     this.combinators,
                     Link<MetadataAnnotation> metadata)
     : super(metadata);
+
+  LibraryDependency asLibraryDependency() => this;
 }
 
 /**
  * An [:import:] library tag.
  *
  * An import tag is dependency on another library where the exported identifiers
  * are put into the import scope of the importing library. The import scope is
  * only visible inside the library.
  */
 class Import extends LibraryDependency {
@@ skipping 298 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);
 }