Fix warnings in dart2js.

dart/lib/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.
 
 /**
  * Pretty-prints Node tree in XML-like format.
  *
  * TODO(smok): Add main() to run from command-line to print out tree for given
  * .dart file.
  */
@@ skipping 377 matching lines @@
     openNode(node, "VariableDefinitions");
     visitChildNode(node.type, "type");
     visitChildNode(node.modifiers, "modifiers");
     visitChildNode(node.definitions, "definitions");
     closeNode();
   }
 
   visitWhile(While node) {
     visitNodeWithChildren(node, "While");
   }
+
+  visitNode(Node node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitCombinator(Combinator node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitExport(Export node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitExpression(Expression node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitGotoStatement(GotoStatement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitImport(Import node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLibraryName(LibraryName node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLibraryTag(LibraryTag node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLiteral(Literal node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLoop(Loop node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPart(Part node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPartOf(PartOf node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPostfix(Postfix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPrefix(Prefix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitStatement(Statement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitStringNode(StringNode node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  unimplemented(String message, {Node node}) {
+    throw message;
+  }
 }