Support parameter metadata.

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 392 matching lines @@
     visitChildNode(node.type, "type");
     visitChildNode(node.modifiers, "modifiers");
     visitChildNode(node.definitions, "definitions");
     closeNode();
   }
 
   visitWhile(While node) {
     visitNodeWithChildren(node, "While");
   }
 
+  visitMetadata(Metadata node) {
+    openNode(node, "Metadata", {
+      "token": node.token
+    });
+    visitChildNode(node.expression, "expression");
+    closeNode();
+  }
+
   visitNode(Node node) {
     unimplemented('visitNode', node: node);
   }
 
   visitCombinator(Combinator node) {
     unimplemented('visitNode', node: node);
   }
 
   visitExport(Export node) {
     unimplemented('visitNode', node: node);
@@ skipping 52 matching lines @@
   }
 
   visitStringNode(StringNode node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }