Fix warnings in dart2js.

dart/lib/compiler/implementation/dart_backend/utils.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.
 
 class CloningVisitor implements Visitor<Node> {
   final TreeElements originalTreeElements;
   final TreeElementMapping cloneTreeElements;
 
   CloningVisitor(this.originalTreeElements)
       : cloneTreeElements = new TreeElementMapping();
@@ skipping 189 matching lines @@
 
   visitTypeVariable(TypeVariable node) => new TypeVariable(
       visit(node.name), visit(node.bound));
 
   visitVariableDefinitions(VariableDefinitions node) => new VariableDefinitions(
       visit(node.type), visit(node.modifiers), visit(node.definitions),
       node.endToken);
 
   visitWhile(While node) => new While(
       visit(node.condition), visit(node.body), node.whileKeyword);
+
+  Node visitNode(Node node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitCombinator(Combinator node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitExport(Export node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitExpression(Expression node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitGotoStatement(GotoStatement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitImport(Import node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitLibraryName(LibraryName node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitLibraryTag(LibraryTag node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitLiteral(Literal node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitLoop(Loop node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitPart(Part node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitPartOf(PartOf node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitPostfix(Postfix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitPrefix(Prefix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitStatement(Statement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  Node visitStringNode(StringNode node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  unimplemented(String message, {Node node}) {
+    throw message;
+  }
 }