Support symbol literals.

sdk/lib/_internal/compiler/implementation/tree/prettyprint.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;
 
 /**
  * Pretty-prints Node tree in XML-like format.
  *
  * TODO(smok): Add main() to run from command-line to print out tree for given
@@ skipping 349 matching lines @@
   }
 
   visitSwitchCase(SwitchCase node) {
     visitNodeWithChildren(node, "SwitchCase");
   }
 
   visitSwitchStatement(SwitchStatement node) {
     visitNodeWithChildren(node, "SwitchStatement");
   }
 
+  visitLiteralSymbol(LiteralSymbol node) {
+    openNode(node, "LiteralSymbol");
+    visitChildNode(node.identifiers, "identifiers");
+    closeNode();
+  }
+
   visitThrow(Throw node) {
     visitNodeWithChildren(node, "Throw");
   }
 
   visitTryStatement(TryStatement node) {
     visitNodeWithChildren(node, "TryStatement");
   }
 
   visitTypeAnnotation(TypeAnnotation node) {
     openNode(node, "TypeAnnotation");
@@ skipping 90 matching lines @@
   }
 
   visitStringNode(StringNode node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }